Tag Archives: Ground Penetrating Radar

Pipe dreams

Yes, I know, blog posts are like busses…

Some of you may have seen a recent BBC News item about the holes for the gas pipe in Verulamium Park.

Fig. 1: BBC News item about Verulamium Park.

I must admit to being a little peeved that a few small roughly dug holes to look at a gas pipe got more media attention than CAGG’s extensive surveys in Verulamium!  The gas pipe has always been, however, the bane of our lives as it’s magnetic field is so strong it masks a 30m wide strip of the archaeology in our magnetometer survey.  That field, however, has no impact on the GPR and I have been intending to extend the GPR survey to cover the areas affected by the pipe. This, and the forthcoming meeting of the Roman Finds Group in Verulamium this Friday, prompted me to see if anyone could come out at short notice and survey around one of the pipe holes.

Fig. 2: Surveying the pipeline (photo: Mike Smith).

So, Mike Smith and I spent a day surveying around the site of the hole in which the traces of a Roman building were discovered.  It got a little fiddly at times, especially as the pipe had to be dragged along 11m every 30 minutes as they joined the lengths together.  The location of our new survey is given in Fig. 3.

Fig. 3: the location of the latest GPR survey shown in red.

As usual, we surveyed in 40m lengths (where possible) at 0.5m transect spacing.  The data were sliced using GPR Process and the images produced using Surfer v. 8, and imported into Google Earth via Adobe Photoshop.  The last step is needed to make the missing bits transparent. Unusually, the deeper slices (nos. 8 and 9) still showed useful information.

One annoying thing is that Google Earth have recently updated the satellite image for Verulamium.  It is a bit dark to my eyes, but more seriously it is in the wrong place.  In the time slices I could see the relationship between the path and the image was clearly wrong.  I spent some time checking my notes, but when I checked the historical imagery, I found the 2009 images matched the plots much better.  I have, therefore, used the older imagery for the figures below.

Fig 4: the magnetometer survey in the area of the new GPR survey.

In Fig. 4 we can see the magnetometer survey for the area in question.  The pipe line, running under the path and then diagonally across the football pitch, dominates the plot.  We can however, see the road running clearly SW–NE across the map (Niblett and Thompson’s Streets 16 and 17 crossing Street 12), and bit of buildings showing as the white lines against the grey and black.  As well as the gas main, there are three pipelines running from the cafe in the NE corner.

Fig. 5: third time slice, 10.5 to 13.5ns.

In Fig. 5, the topmost time slice in the sequence, we can already see the road surface running SW–NE, and we can also see signs of the pipe running across the plot although this might be a marker in the upper levels as the pipe itself shows more clearly lower down.

Fig. 6: fourth time slice, 13.5 to 16.5ns.

The next slice (Fig. 6) shows the road more clearly, and some hints of buildings.  I am unsure what the area of high reflections is to the south-east and parallel to the road is.  It is almost as if the road line was changed a little at some point.

Fig. 7: fifth time slice, 16.5 to 19.5ns.

Fig. 7 is starting to show the buildings up near the path much more clearly.  These are buildings that front onto Street 12 to the north.  Street 12 eventually leads into the forum and is probably part of Watling Street.  At the southern edge of the survey there are some white areas which may be robbed walls, with perhaps a surviving floor surface.

Fig. 8: sixth time slice, 19.5 to 22.5ns.

In Fig 8. we can now see two very clear lines either side of the road.  These maybe stone conduits or roadside drains?  The buildings near the path are starting to show more clearly, and now we can see the gas pipe quite clearer.  The fact that is disappears to the west is probably due to topography.  Ideally, time slices would be topographically corrected.

Fig. 9: seventh time slice, 22.5 to 25.5ns.

Fig. 9 shows the gas main beautifully, and more of the buildings near the path.  Those to the east of Street 16 and south of Street 12 are labelled “baths” by Niblett and Thompson.  The GPR data would make that interpretation a little more tentative, I think.

Fig. 10: eighth time slice, 25.5 to 28.5ns.

Fig. 11: ninth time slice, 28.5 to 31.5ns.

Figs 10 and 11 show some of the deeper features.  Some hints of more buildings are showing, especially in the NW corner of the plot.

Personally, I think this is much more interesting and informative than the gas pipe trench!

Fig. 12: the gas pipe.

The one thing that will be useful, is that by knowing how deep the gas pipe is below the surface, we can calibrate the speed of the GPR signal and convert nanoseconds into depth.

I am hoping to continue to expand the GPR survey when I can over the coming months.

Many thanks to Mike for coming out for the day in the cold sunshine.

Filling in the gaps

Thanks to Stuart Gray of Strutt and Parker, I was able to contact Pete and Fiona Letanka and obtain permission for us to survey the paddock of Darrowfield House which lies immediately behind Verulamium Museum. It is the last large-ish area of Verulamium left that has not been totally surveyed using magnetometry. Members of CAGG are, therefore, spending this week filling in the gap.  Our mag was away being repaired, but Pat Johnson of Foerster kindly agreed to bring it down to us today.  We started, therefore, with Earth Resistance and GPR, but after lunch the poor old res meter was left abandoned on the grass while the team got started with the mag survey.

The paddock ought to be exciting.  It lies just behind the line of the Roman wall, and there is a road shown in publications running SW-NE across it.  The first mag results are shown in Fig. 1.

Fig. 1: the mag survey.

They are surprisingly unexciting.  The diagonal lines running SW-NE look like cultivation marks of some sort.  There is a quiet area behind the supposed line of the wall, running NW-SE, and then one high-magnetic curved feature which may match a bank we can see in the field.  No real sign of the wall, or of the road,

The GPR survey has been processed in 3ns thick slices.  As usual, I’ll work my way down from the top.

Fig. 2: GPR survey, time slice 3, from 10.5ns to 13.5ns.

Fig. 3: GPR survey, time slice 4, from 13.5ns to 16.5ns.

The third slice shown in Fig. 3 really shows surprisingly little. I’m guessing we are only looking into the topsoil here.  The fourth slice (Fig. 3) starts to show some diagonal striping similar to what we can see in the mag data.  Again, this is probably agricultural.

Fig. 4: GPR survey, time slice 5, from 16.5ns to 19.5ns.

Fig. 5: GPR survey, time slice 6, from 19.5ns to 22.5ns.

The fifth slice (Fig. 4) shows the striping very strongly, with two alignments at right angles.  I think these must be land drainage.  They look too straight for “ridge and furrow” and do not have a headland. What is also interesting — or is that worrying? — is that the wheel-ruts which show so clearly on the Google Earth image in the background, also show in the GPR data at this depth.

The sixth slice (Fig 5) faintly shows echoes of the drainage.  To the north are some black squiggly features.  Yes, folks, we have mapped the badger setts!  Nothing very archaeological, so far.

Fig. 6: GPR survey, time slice 7, from 22.5ns to 25.5ns.

In the final slice (Fig. 6), we still have the setts in the north, but we have a very strong linear feature to the south running SW-NE.  Comparing this to the proposed line of the road in Fig. 7, we can see that this would appear to be one edge of it.

Fig. 7: GPR survey, time slice 7, from 22.5ns to 25.5ns, with overlain map of Verulamium.

Right at the edge of the GPR’s signal depth where the returns are very attenuated, we are starting to see the archaeology. Unfortunately, I cannot yet easily convert the time (22.5ns–25.5ns) into physical depth.  It would seem, however, that the archaeology in the lower area may well be at the limit of what we can pick up.  If we look at the radargrams, however, we can see a big feature running across our vertical slices and I would guess this is the road surface.

Fig. 8: an example radargram showing the possible road.

Many thanks to everyone who turned out today and enjoyed the beautiful sunshine.  Also, big thanks to Pat for bringing the mag back for us, and Pete and Fiona for arranging for us to be able to survey the Paddock.

There probably won’t be a posting tomorrow, but I hope on Weds to catch-up.

Four days in the Park (part 1)

A combination of members of CAGG and students from the Institute of Archaeology, UCL, undertook four days of survey in Verulamium Park a couple of weeks ago.  It was supposed to be five days, but the Saturday was called off because of rain.  We aimed to:

  • extend the magnetometry survey into Abbey Orchard, the field between the Park and the Cathedral;
  • undertake some more GPR survey in the Park;
  • try the six-probe six-depth method of Earth Resistance survey over one of the buildings we have previously surveyed;
  • try a resistivity psuedo-section across the line of the town wall near St Germain’s Block.

It was definitely one of “those” survey periods.  Every single technique had some problem or other of varying degrees of seriousness.  We managed to sort most of them out in the end, but that and the Archaeology in Hertfordshire: Recent Research conference which was held on Saturday 26th have delayed this posting.

I am going to post the results in two parts, starting with the mag and GPR data.

The mag survey

The area being surveyed is not very large, but is quite awkward.  It lies on a steep slope, has many trees and a great number of people walking by.  It should, however, have evidence of the abbey, and possibly a late Roman cemetery.  It also may have an Iron Age enclosure which was seen on an aerial photograph, and maybe the early Saxon town.

Fig. 1: The survey team in Abbey Orchard.

Fig. 1: The survey team in Abbey Orchard.

Between teaching, equipment issues and rain, we didn’t get as much done as we hoped, but we have at least started on this, our first extramural area at Verulamium.

Fig. 2: the mag survey results.

Fig. 2: the mag survey results.

Very little can be seen in this plot.  It is very “noisy”.  There is one potential thin feature, and the vague hint of a larger, wider feature (marked with red arrows in Fig. 2).  Given where we are working, this is all very disappointing so far.  We do need to complete this area if we can, however, so we’ll be back at some point.

The GPR survey

We did have some problems with the GPR as well, but eventually we managed to resolve those and completed an area 160m by 40m on the southern side of the town near the London Gate.  The weather and obstacles could prove challenging (Fig. 3).

Fig. 3: GPR survey in the Park, November 2016.

Fig. 3: GPR survey in the Park, November 2016.

As usual, I used Larry Conyers and Jeff Lucius’ free software to “time slice” the GPR data.  I created 3ns thick slices which seem to work well at Verulamium.  The third slice (10.5–13.5ns; Fig. 4) shows features close to the ground surface.  The dark smear running NS is the topmost layers of Watling Street.  The diagonal lines, which also show in the magnetometry data, must be some sort of drainage.

GPR time slice 3 (10.5--13.5ns).

Fig 4: GPR time slice 3 (10.5–13.5ns).

The next slice (13.5–16.5ns, Fig. 5) shows the archaeology much more clearly.  Watling Street is the black north-south feature to the east of the plot.  There is, however, a hole in it!  I guess this is another example of the extensive robbing of the town for building materials.  Slightly to the west, a narrower minor road is running SW–NE across the plot.  This road lines up with the light linear feature in the mag data.  On the north side of this smaller road is a building with at least two rooms and what appears to be a paved area to the NE.

GPR time slice 4 (13.5--16.5ns).

Fig 5: GPR time slice 4 (13.5–16.5ns).

Slice 5 (16.5–19.5ns; Fig 6) still shows Watling Street and the building.  There is a hint of some linear features that are on the same alignment as the rectangular enclosure which shows in the mag data to the south, and a wall in the SE corner.

GPR time slice 5 (16.5--19.5ns).

Fig 6: GPR time slice 5 (16.5–19.5ns).

The next slice (Fig. 7; 19.5–22.5ns) as there are hints of robbed walls showing in the south side of the plot next to Watling Street.  These are showing as white lines of reflection free data and do seem to form structures of some sort.  These align with the strange enclosure seen in the mag data.

GPR time slice 6 (19.5--22.5ns).

Fig. 7: GPR time slice 6 (19.5–22.5ns).

The last slice (Fig. 8, 22.5–25.5ns) is interesting in that the main line of Watling Street is still visible, but does not have such strong reflections as before.  There are, however, two bands of strong reflections either side of the road.  Perhaps these are the roadside ditches known from excavation filled with rubble from the road surfaces and construction?  The signal at this depth has started to attenuate and I will not show the deeper slices.

GPR time slice 7 (22.5--25.5ns).

Fig. 8: GPR time slice 7 (22.5–25.5ns).

In Part 2 I will show the results of the two electrical techniques.

Ellen has designed a logo for CAGG.  What do you all think?

cagg-logo-3

T-shirts anyone?

Durobrivae

Just to the west of Peterborough lies the Roman town of Durobrivae. This town is one of the so-called ‘small towns’, i.e., not one of the public towns with an administrative function.  It is, however, somewhat larger than some of the public towns such as Caistor-by-Norwich, the civitas-capital of the Iceni.  Duriobrivae had a town wall, parch marks from which can be seen on the Google Earth image along with Ermine Street (the straight line through the town from SE to NW) and the irregular street plan (Fig. 1).

Fig. 1: Google Earth image of Durobrivae.

Fig. 1: Google Earth image of Durobrivae.

Oblique aerial photography over the years has revealed much about the interior of the town, as well as extensive suburbs, prehistoric features, villas and so on.  Fig. 2 shows an oblique image of the town.

Oblique aerial photograph of the town. Reproduced courtesy of Stephen Upex.

Fig 2: Oblique aerial photograph of the town. Reproduced courtesy of Stephen Upex.

I was particularly fascinated to see a large group of circular features to the south of the town, some of which appear to be the ditches around round-barrows, but others are far too large and are tentatively suggested to be some form of henge (Figs. 3 and 4).

Fig. 3: Google Earth image of the field to the south of the town showing circular prehistoric features.

Fig. 3: Google Earth image of the field to the south of the town showing circular prehistoric features.

Fig. 4: Oblique aerial photograph of the field to the south of the town showing the Roman suburbs and earlier prehistoric circular features. Photograph courtesy of Stephen Upex.

Fig. 4: Oblique aerial photograph of the field to the south of the town showing the Roman suburbs and earlier prehistoric circular features. Photograph courtesy of Stephen Upex.

Ruth Halliwell (WAS), who has worked with CAGG regularly, is working on the town for her dissertation and we arranged to go and team-up with local archaeologists to undertake some survey.  It was very much a “proof of concept” trip: which techniques would work best there? Would the surveys add to what could be seen from the air?  We undertook three days survey running all three main machines (magnetometry, resistance and GPR), and Peter Alley also used his UAV to take high-level photographs, partly with a view to creating topographic maps.

Despite early problems with the mag, we managed to survey an 80m wide, 360m long strip NS across the town.  The overall results can be seen in Fig. 5.

Fig. 5: the magnetometry survey.

Fig. 5: the magnetometry survey.

There is a great deal going on in the results.  Ermine Street shows clearly running across the NE corner of the survey transect and matches the parch mark beautifully.  Either side of Ermine Street are a series of buildings with their gable ends onto the road in the approved Romano-British manner.  Other streets can be seen, again matching the parch marks.  Not all the buildings are so clear, but there are clearly other walls that can be seen in the data.  Towards the south, the pattern is more complex.  The results could be cleaned-up a little more.  In places we were suffering from some stagger, partly as a result of the fine reddy-brown dust that settled over all the machines and their operators  (Fig. 6) which, combined with the lubricant we use on the cogs, turned to a sticky slurry.

Fig. 6: the red dust all over the GPR. Image courtesy of Mike Smith.

Fig. 6: the red dust all over the GPR. Image courtesy of Mike Smith.

We undertook a radar survey using the Mala GPR we have on loan from SEAHA.  Pushing the GPR was quite hard work in the long grass, especially as one goes over the agger on which Ermine Street appears to have been constructed (Fig. 7).  The team did, however, manage to complete an excellent six blocks of data.

Fig. 7: Pushing the GPR over Ermine Street.

Fig. 7: Pushing the GPR over Ermine Street.

The images on the screen of the GPR shows that we were getting reasonable depth penetration. I created amplitude maps in 3ns thick slices.  The third slice map (Fig. 8) clearly shows the surface of Ermine street, but for most of the area surveyed the radar signal is still in the ploughsoil.

Fig. 8: time slice 3, 10.5-13.5ns.

Fig. 8: time slice 3, 10.5-13.5ns.

In the fourth time slice (13.5–16.5ns, Fig. 9)  some of the other roads are starting to show, and odd bits of wall.  One very curious feature is the lighter coloured band across the middle of the southern area.  Although it would appear to be related to our grid, our survey was conducted NS across that band.  The aerial photograph (Fig. 2) does show a band across the field so perhaps this is related to some sort of cultivation pattern?

Fig. 9: time slice 4, 13.5-16.5ns.

Fig. 9: time slice 4, 13.5-16.5ns.

The fifth slice (16.5–19.5ns) shows more details in the buildings (Fig. 10).  In the centre of the lower block is a square feature.  This is the Romano-Celtic temple known from aerial photographs.  This type of temple, well-known from many sites across the north-western provinces of the Roman Empire and consists of two concentric squares, usually reconstructed as an inner sanctum and an outer ambulatory.  The two roads the the north and south of the temple appear to mark the edges of the temenos or sacred precinct.  There is a hint of a possibly paved area to the west of the temple, and a solid feature between the internal and external walls to the east.  In the northern block there are hints of the walls on either side of the road as seen in the magnetometry data.

Fig. 10: time slice 5, 16.5-19.5ns.

Fig. 10: time slice 5, 16.5-19.5ns.

In the sixth time slice (19.5–22.5ns) we can start to see some of the buildings along Ermine Street not, as I had expected, as black ‘high amplitude’ features shown in black i.e., stone walls, but as low amplitude features, i.e., areas which have fewer items that would reflect radar waves (Fig. 11).  At Verulamium, I have interpreted these as where the stone foundations have been robbed, but here we know less about the construction techniques used.  Part of the difficulty is that Ermine Street is on a quite marked bank which means the radar has a greater depth of deposits to penetrate.  I undertook a topographic survey of just the northern block area (Fig. 12) and in the future will be able to process the GPR data taking into account the topography.

Fig. 11: time slice 6, 19.5-22.5ns.

Fig. 11: time slice 6, 19.5-22.5ns.

Fig. 12: topographic survey of the northern block.

Fig. 12: topographic survey of the northern block.

In the seventh and eighth time slices (22.5–25.5ns, 25.5–28.5ns), the GPR radar waves are starting to attenuate and we are getting quite faint reflections, but some of the deeper foundations show in these lower time slices (Figs. 13–14),  For example, some of the buildings along Ermine Street start to show very well in Fig. 13, and the outer wall of the Romano-Celtic temple shows very well in Fig. 14.

Fig. 13: time slice 6, 22.5-25.5ns.

Fig. 13: time slice 6, 22.5-25.5ns.

Fig. 14: time slice 6, 25.5-28.5ns.

Fig. 14: time slice 6, 25.5-28.5ns.

There is a great deal more which can be extracted from the GPR data, especially by looking at the radargrams (the vertical slices) and comparing them to the time slices.  The results are less “black and white” than at Verulamium and quite complex, but there is a great deal going on in this data which will take a bit of work to tease out all the details.

As well as the magnetometry and radar surveys, we undertook a resistance survey using UCL’s new RM85 meter (Fig. 15).  We took readings every 50cm.  We managed to survey an area 60x by 80m which had also been surveyed using the GPR and the magnetometer.

Fig. 15: Richard Cushing and Stephen Upex working on the resistance survey.

Fig. 15: Richard Cushing and Stephen Upex working on the resistance survey.

The result of this survey was quite surprising (Fig. 16).

Fig. 16: the earth resistance survey.

Fig. 16: the earth resistance survey.

The square within a square plan of the Romano-Celtic temple could not have been more obvious.  The small room on the eastern side, partially seen in the GPR survey, shows clearly.  The temenos is also quite clear.  A spectacular result, but one that raises a question. Why is the inside of the temple such low resistance?  Normally, low resistance like this is related to water retention.  Is the outer wall of the temple causing water to pool within the wall?  It is useful to compare the three surveys (Fig. 17).

Fig. 17: comparing the three survey techniques and the parch marks in the area of the temple.

Fig. 17: comparing the three survey techniques and the parch marks in the area of the temple.

It will take a bit of work to draw-up a composite interpretation plan.

Peter Alley also undertook some surveys with his UAV (Fig. 18).

Fig. 18: Peter Alley using his UAV to map the site.

Fig. 18: Peter Alley using his UAV to map the site.

As well as taking high-level images of sites, the UAVs pictures can be used to create topographic models using a technique called “Structure from motion”.  Fig. 19 shows a topo plan of part of the site derived from the photographs.  The actual heights vary from my plan because the UAV’s plan needs to be corrected against some control points, but the relative heights are great.  This technique is going to prove very useful in future.

Fig. 19: Topo map in QGIS derived from the UAV's aerial imagery.

Fig. 19: Topo map in QGIS derived from the UAV’s aerial imagery.

The aim of this three days of fieldwork was simply to see which survey techniques would provide useful information at this site.  The answer is: all of them!  We already have a huge amount of data to examine in more detail, and a great deal of thinking to do.  It certainly seems that a more extensive programme of geophysical survey would add to our knowledge of the town greatly, as well as other archaeological features such as the “henges” to the south.

As always, many thanks indeed to everyone who came to help, especially Mike Smith for transporting and running the GPR, and Jim West for helping to run the mag.  This was a great team effort between local group members and CAGG, and exactly what our group exists to do.

Fig. 20: the end of day.

Fig. 20: the end of day.

Rain didn’t stop play

… but may be it should have done!  Last year, on the last day of the survey, it poured and we cancelled.  Today, we thought “it is only a little drizzle!”  On occasions, drizzle was more of a deluge.  At one point I was about as far from the cars as it is possible to get when on site, and I got soaked.  Thankfully, Ellen went and fetched a dry tee-shirt and my waterproof coat.  Thank you Ellen, you’re a star!

Peter, one of our volunteers from SWHAS and WAS, has bought himself a UAV fitted with a camera.  He has been having some practice flights over the workers and the site.  When I have worked out how to edit the video down to a sane size, I’ll post one of those, but meanwhile here is one of the stills.  The UAV will prove a very useful tool.

Verulamium Theatre.

Verulamium Theatre.

One of the main reasons we persisted in the rain was the fact that we are so very close to completing the mag survey of the Macellum field.

The magnetometer survey of the Macellum field.

The magnetometer survey of the Macellum field.

Here is a closer detail of today’s survey.

The mag survey after day 36.

The mag survey after day 36.

As can be seen, Watling Street has rejoined the drive.  There appear to be many buildings opposite the theatre which isn’t a surprise in the heart of the town.  Street 24, which runs NNE from the theatre, has the macellum on the east side of it.  This building has been partially excavated and has a complex building history of five phases going from the mid-first century to the early fourth.  It has an almost equally complex excavation history: it has been examined by Grove Lowe (1847), John Harris (1869), Kathleen Kenyon (1934) and finally by Miss K. M. Richardson in 1938.

The resistance survey continued.  The wet surface was both a boon and a problem.  The first two grid squares went very smoothly.  Then we moved all the probes and so forth and the machine started to play-up.  After lunch, Peter came to the rescue and worked out that there was water where it oughtn’t to be, cleaned and dried connections and so forth, and all was well again.  We managed another three grids including one in 35 minutes.  Here is the survey.

The res survey after day 36.

The res survey after day 36.

The same area as the previous image showing the mag data.

The same area as the previous image showing the mag data.

In the first of the two images, I have not “edge matched” the grids so that you can see the ones which are a problem.  Three of the grids we did today fixed existing problems.  Although we had not planned to work tomorrow, I am hoping we might manage five more squares to fix the problems and give us a nice tidy survey.  Archaeological geophysicists are obsessed by “nice tidy surveys.”

Comparing the mag and the resistance surveys, the end of the “sinuous ditch”, seen snaking in from the top of the mag survey, can be seen in the resistance survey but it seems to continue further to the east.  The clear building on the northern edge of the resistance plot also shows pretty well in the mag survey.

Lastly, we learnt one lesson today.  The GPR doesn’t work well in the rain!  We surveyed a block near the rectangular enclosure I thought might be a temple.  Here is the mag:

Rectangular enclosure, near the southern side of the town, seen in the mag data.

Rectangular enclosure, near the southern side of the town, seen in the mag data.

Speculation has been rife as to what this may be, so we tried using the GPR.

Day 36 GPR data.

Day 36 GPR data.

The terrible striping is caused by the rain.  We will have to re-do this block another year.  We can see, however, a square in the centre of the block, and almost another square around it. Before we get too excited, however, comparison of the two surveys shows that the squares in the GPR data lie outside the NNE edge of the enclosure, and in fact, partly show as light white lines in the mag data.  Yet another question to be investigated more fully next year.

Many thanks to everyone who suffered the rain today.  You are all stars.

Tomorrow will be our last day.  I won’t post the results until Tuesday, however, as we are going for a celebration meal in a local pub.

Three day catch-up

I haven’t managed a Verulamium post for a few days so here is a quick catch-up.

Firstly, the mag has been slowly working its way eastwards along the Macellum Field.  They are getting pretty close to the end of it.

The mag survey in the Macellum field after day 35.

The mag survey in the Macellum field after day 35.

As can be seen, Watling Street stands out very clearly running from near the theatre to the Chester Gate.  There are lots of buildings along the road as would be expected.  Some are less clear than one would hope because they have been partially excavated.  The spec-ally look to the data, almost certainly because of the gravel subsoil, does make it harder to see what is going on here.  The carrot at the end of the stick — apart from just finishing the field of course — is that there are two Romano-Celtic temples known from aerial photographs near the modern road.

The next image is just to show how much of Verulamium we have now completed.  Poster, anyone?

The complete survey so far.

The complete survey so far.

The resistance survey has had a few problems.  The lack of rain has made the top-surface of the field very dry and hard.  It is very slow going, and the data is not as clean as one would like.  Despite the problems, however, some of the buildings along the road, especially at the north side of the plot, are very clear indeed.

The resistance survey after day 35.

The resistance survey after day 35.

Although it doesn’t jump out at one when just looking at the plot, the sinuous ditch does show in the resistance data when one knows where to look!

The GPR team completed some blocks along the hedgeline which I haven’t processed yet… sorry!  They also did one block up next to the Chester Gate to investigate the building here, and one over the sinuous ditch.  The latter did show the ditch but very little else.  Let’s look at the block near the Chester Gate.

The mag survey near the Chester Gate.

The mag survey near the Chester Gate.

This first image shows the mag data.  The building in the middle shows as white lines roughly parallel to the modern drive.  There are lots of other darker features, probably various pits and the sinuous ditch shows to the west.

Day 35 GPR, slice 2 (9.5 to 12.5ns).

Day 35 GPR, slice 2 (9.5 to 12.5ns).

This time slice shows the impact of splitting the survey over two days!  The left hand side was done yesterday afternoon, the right hand side this morning.  The pattern of the ploughing and the tractor’s turning circle in the corner of the field show clearly.  Luckily, the problem is much less acute at lower depths.

Day 35 GPR, slice 3 (12.5 to 15.5ns).

Day 35 GPR, slice 3 (12.5 to 15.5ns).

This time slice now shows the building beautifully.  What a wonky end wall on the north side! There is a long narrow range of rooms to the SW.

Day 35 GPR, slice 4 (15.5 to 18.5ns).

Day 35 GPR, slice 4 (15.5 to 18.5ns).

This time slice shows the SW line of rooms more clearly, although at the southern end they are been partly destroyed.  We can see, however, fainter traces of the walls on the NE, a corridor, perhaps?

Day 35 GPR, slice 5 (18.5 to 21.5ns).

Day 35 GPR, slice 5 (18.5 to 21.5ns).

This time slice does show the “corridor” to the NE much more clearly.  Perhaps it is more deeply buried in the plough bank?   For most of the plot, though, nothing much else is showing.

There has been a little rain this evening.  I have my fingers crossed for more.  Hopefully, tomorrow will be dry so that the mag can plough on eastwards!

As always, many thanks to everyone, especially those working with the res meter.  It is slow and boring at the best of times, but slow+annoying is a great deal to ask.

Lamer Park

This post is dedicated to the memory of David Gifford of Lamer (1942–2016).

Lamer lies a mile north of the village of Wheathampstead on the edge of the parish.  The name Lamer is first attested in 1396 in a document held by Westminster Abbey.  Westminster held the manor of Wheathampstead, a gift from Edward the Confessor in 1060.  The original deed is held in the Hertfordshire Archives and Local Studies centre (HALS).  Lamer became a manor in its own right in the fourteenth century.  The earliest mention of a Park at Lamer dates to 1589 (information from Anne Rowe).  The manor house is claimed to have been rebuilt by Sir William Garrard around 1555.  Only one drawing of this earlier house survives, but some sources doubt its accuracy. His grandson, Sir John Garrard became the first baronet, and the tombs of all six baronets are in St Helen’s Church, Wheathampstead.

The tomb of the Sir John Garrard, 1st baronet.

The tomb of the Sir John Garrard, 1st baronet.

On the death of sixth Baronet, Sir Benet Garrard (c.1704 to 1767), the baronetcy lapsed and the estate passed to  Charles Drake, who adopted the name Drake Garrard.  They began the remodelling of the the estate replacing the Jacobean house with an elegant Georgian one.  They also employed Nathaniel Richmond to remodel the Park.  When Richmond died, the task fell to Humphrey Repton who created one of his famous “red books”.  According to the Dury and Andrews’ map of 1766, the Park then consisted of a series of avenues of trees as had been the fashion in the late 17th/early 18th century.

Lamer Park from Dury and Andrews' map, as redrawn by Andrew Mcnair.

Lamer Park from Dury and Andrews’ map, as redrawn by Andrew Mcnair.

The remodelling of the Park by Richmond and Repton created a more open “natural” landscape as was the fashion towards the end of the 18th century.  Maps held by Westminster Abbey (1799) and HALS (1827) show the Park as a much more open landscape.  This is also reflected in the tithe map, and an estate map from 1843 held by the Gifford family.

Map of Lamer from 1843.

Map of Lamer from 1843.

The Estate was inherited by Apsley Cherry in 1892 who changed his name to Cherry-Garrard in accordance with the terms of the inheritance.  His only son was the famous arctic explorer, Apsley Cherry-Garrard.

The monument to Apsley Cherry-Garrard in Wheathampstead church.

The monument to Apsley Cherry-Garrard in Wheathampstead church.

Apsley slowly sold off the estates belonging to Lamer, and finally sold the house and Park just after the Second World War.  The house was demolished in 1949 and the Park turned into farmland.

One might ask how geophysics comes into all this?  Many of the buildings in the 1766 and later maps still survive.  On the Dury and Andrews map, however, there is a small building with, perhaps, a wall and garden just to the east of the main buildings.  This building is otherwise unknown.  In June, Mike Smith and I undertook a small GPR survey in the field to the east of the coach house in the hope of locating this building.  We only surveyed one small 40x40m block, so it was a bit of a long shot.  Here are the time slices.

The 7 to 9ns time slice.

The 7 to 9ns time slice.

The 9 to 11ns time slice.

The 9 to 11ns time slice.

The 11 to 13ns time slice.

The 11 to 13ns time slice.

The 13 to 15ns time slice.

The 13 to 15ns time slice.

The 15 to 17ns time slice.

The 15 to 17ns time slice.

The 17 to 19ns time slice.

The 17 to 19ns time slice.

We have, I think, essentially found the remains of three roads.  The road which shows clearly in the SW corner, especially in the 9–11ns time slice, was known.  Angela Gifford remembers this road being built as a child in the early 1950s.  More curious are the other two roads.  The east-west road, that also shows clearly on the 9–11ns time slide, appears to line up with the existing tarmac road.  That road, however, was created relatively recently by David.  Was there an earlier version of it?  There wasn’t, originally, access between the two buildings north and south of the tarmac road.  A plan at HALS shows the gap filled with the a building for the dung from the coach house and stables (to the south of the current road) and the hack stables to the north. The third road is the broad curving line running from the SE corner of the plots to the middle of the northern edge.  This road is unknown to the current inhabitants of Lamer.  Map evidence shows that the road system was changed quite frequently between the late 18th century and now.  This road must have been part of the Park at an earlier date.  In the deeper time slices, e.g., the  15–17ns one, one edge of the road appears as a series of dots.  I think this is just because Mike and I were surveying north-south and the interpolation algorithm has not managed to join them up when the line is at such an acute angle to the line of the transects. There does, however, seem to be “something solid” edging the road on the eastern side.

We didn’t find the house and courtyard, but it was not entirely a bust either.  Perhaps we should do some more!

Dave’s family have been raising money for the Hertfordshire Air Ambulance in his memory. Please donate to this worthy cause if you can.