Tag Archives: Roman town

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.

Another day, another town

You would think I would have had enough. But no… hot on the heels of the end of the Gorhambury season, we headed off to the mysterious east side of the county. The Greenwich meridian seems to exert a powerful influence in Hertfordshire with its citizens seemingly afraid to cross the invisible line.

Back at the start of the project, we planned to do some survey in and around Braughing.  We managed just one site. The area is extremely important with multiple late Iron Age and Roman sites including the Roman “small town” on Wickham Hill.  We had an opportunity to work on the small town along with members of the Braughing Archaeological Group for a couple of days, mainly to see if magnetometry would show something useful.  The field was, however, rather rough and caused the odometer on the cart to over-run by about a meter, and the nuts and bolts needed constant tightening. On the second day I adjusted the odometer settings which improved matters a bit.

The survey underway on Wickham Hi

The survey underway on Wickham Hill.

We managed to complete 13 grid squares which was pretty good going, especially as the data logger crashed three lines before the end of the fourteenth square and we lost the rest of the grid.  The results, after a bit of work in TerraSurveyor, were very interesting.

The survey results.

The survey results.

The broad line running east-west towards the south of the surveyed area is the road.  It can be seen in the Google Earth image in the background.  Towards the west, the very dark band must be where the road becomes a sunken way as it goes up the slope.  What is very obvious is the difference to the planned public town at Verulamium.  This site was clearly a very different type of settlement.  What we have clearly shown is that it is worth expanding the magnetometry survey to cover as much of the settlement as possible.  Hopefully, the field surface will be a little more benign when we return!  One thing won’t change, however, and that is the slope…

On top of the hill.

On top of the hill.

Many thanks to Jim West for coming all the way from Chorley Wood to run the mag on the first day while I lay-in the grid, and also many thanks to all the members of BAG who joined in. Looks like we’ll be back!

A picture is worth a 1000 words

The Verulamium magnetometry survey.

The Verulamium magnetometry survey.

I suppose I cannot really get away with that simple a post.

First of all, CONGRATULATIONS to everyone, it is a fantastic achievement and I am so proud of all of you.  Secondly, a big thanks to everyone who turned out for an extra day on Bank Holiday Monday to complete the Macellum field.

How about some numbers?  Well, Verulamium is the third biggest Roman town in Britain, after London and Cirencester.  It is, however, the largest Roman town in Britain which doesn’t have a modern settlement built over most of it.  We have surveyed 64.5ha of the total area of 81ha.  It has taken us 83 working days starting in the summer of 2013, but we didn’t do much at Verulamium in 2014.  It took 12,900,400 readings to cover those 64.5 ha.   That, of course, doesn’t include the grids we did twice because of frozen sensors or other problems. People pushing the cart walked about 322km, not including having to go back to the start for partials, getting to the squares in the first place, or laying in the tapes and strings.

Let us look in more detail at the last bit surveyed in the Macellum Field.

The area surveyed during day 37) high contrast).

The area surveyed during day 37) high contrast).

Several things come to mind.  Firstly, there is very little there!  Towards the NE and along the western side there may be a ditch feature, although it is quite faint.  Other than that, the main (and annoying) thing are the strong magnetic anomalies along the edge of the field.  Some of you may remember the 12″ gas main which runs across the Park… well here it is again.  What I do not entirely understand why there are differences between the negative and positive readings along our grid lines.  Jim and I spent some time making sure I put the composite together correctly, and we are sure it isn’t a survey error.

This end of the field is know to contain two Romano-Celtic temples.  These are known from aerial photographs taken in the hot summer of 1976.  I wonder if this area of the town was kept clear of encroaching buildings, pits, ditches and the like deliberately?  If we turn the contrast down (i.e., clip the image at +/- 40nT instead of +/- 7.5nT, we can see one of the temples close to the hedge as a faint white line.

Low contrast version of the area surveyed on day 37.

Low contrast version of the area surveyed on day 37.

Yet another target for the GPR next year!

Some of the team (many thanks Ellen, Mike and Jim!) helped re-do a number of areas of the res survey, plus one extra bonus square.  The biblical deluge of Sunday night (Lamer Lane was flooded once more) was not ideal.  This is the final area completed in 2016:

The 2016 resistance survey.

The 2016 resistance survey.

It is a pretty good result.  There is almost no use of the “edge match” feature of the software to get the various grids to join neatly.  It could be improved.  The very high contrast of the temple rather makes the buildings faint, but either the creation of selective composites (i.e., processing bit of the survey separately), or use of a high pass filter, would improve that.  The survey is quite big for a res survey: 2.5739ha according to TS (or 2.6ha to sane people who round numbers), which equals about 103,000 resistance readings.  That, of course, doesn’t include the large numbers of squares we re-did due to the dry conditions.

There is a great deal more to do in terms of data processing and interpretation, but I think we all deserve a well-earned rest.  Well, at least until Thursday…!

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.

Record breaking

It was an odd day, weather wise. Largely dry with just one quick, light shower, windy at times, sunny spells… Luckily nothing interfered with the fieldwork!

The res team consisted of myself (when I wasn’t putting in grids for people), Ellen, Tim and Pauline.  They pulled out the stops and managed a record-breaking eight grid squares.  Area-wise, that is what the GPR covers in an average day, but for resistance survey at 0.5m intervals, that is very good going.  Well done everyone.

The resistance survey at the end of day 32.

The resistance survey at the end of day 32.

Today’s grids behaved themselves and make the four odd ones from yesterday stand-out even more.  I did make sure that some of the connectors were off the ground today.  How annoying. We may have to re-do those four grids.  The survey did, however, show the buildings along the road in the SE corner beautifully.  The big question… where now?  North to the sinuous ditch?  South for more shops?  West to cover the cross roads?  Only four days surveying left, and we have to assume that we won’t cover eight squares every day.

The mag team also had a very successful day in the Macellum field.

Detail of the mag survey showing the Macellum field.

Detail of the mag survey showing the Macellum field.

We can just see a hint of the cross-roads running NE-SW across Watling Street.  The ‘1955 ditch’ barely shows.  With the eye of faith one might see it in the high readings along the edge of the cross-road, but very much with the eye of faith.  Is the ditch just so built over we cannot see it?  Or was it never built here?

With just four survey days left to go, the team is getting close to finishing the field, but I think we are a day or two short of being able to do that.

The entire mag survey to date.

The entire mag survey to date.

Way down across the field, the GPR team tackled another fiddly staggered bit along the hedge line.  In the next three images I have made the previous days’ surveys partially transparent.

The day 32 GPR, slice 3 (12.5 to 15.5ns).

The day 32 GPR, slice 3 (12.5 to 15.5ns).

The day 32 GPR, slice 4 (15.5 to 18.5ns).

The day 32 GPR, slice 4 (15.5 to 18.5ns).

The day 32 GPR, slice 35 (18.5 to 21.5ns).

The day 32 GPR, slice 5 (18.5 to 21.5ns).

The curious shallow valley to the west of the surveyed area (‘valley’ seems a strong word for it!) that runs down the hill towards the temple is just as devoid of buildings or other recognizable archaeological features as the mag data.  In all three time slices not a great deal shows.  Was this valley always empty?  Or has the archaeology been eroded away, or even buried?  Difficult to say,  There is, however, a long narrow building just to the right of the middle of the surveyed area almost parallel with the hedgerow.  It seems fairly ephemeral, but it definitely there and one corner was picked-up in last year’s grid to the south.

Although the GPR hasn’t covered as much as the mag, we have still collected a mass of data.

Montage showing the area surveyed with the GPR to date.

Montage showing the area surveyed with the GPR to date.

It certainly takes-up a large chunk of my hard disk.

Many thanks to everyone who came out today and worked so hard.  A very successful day all round.  Our next survey day is on Thursday.

I think we found a building…

Today we managed to run all three instruments despite the very blustery weather and the occasional shower. Many thanks to everyone who put up with the bad weather.

Firstly, the magnetometer survey went very well today with another nine grid squares completed, albeit there were many partials!  Here are the results:

The mag after day 31.

The mag after day 31.

As can be seen, the nice straight line of Watling Street continues running from the SE to the NW. Curiously, there appears to be something cutting across the street and running down either side (shown as white lines).  How strange.  The star find, however, is the very nice building parallel to Watling Street.  The wall foundations show as clear white lines against the mid-grey, i.e., non-magnetic wall foundations (or foundation trenches) cutting through the more magnetic background.  Just in case anyone is wondering where the building is:

Today's mag showing the building.

Today’s mag showing the building.

OK, I’m not being entirely serious.  It is perhaps one of the clearest buildings I have seen in our mag data despite the rather noisy background.

The GPR crew were working quite some distance away.  Here is a location plan:

Location of the three surveys.

Location of the three surveys.

It is 550m from the magnetometer survey to the GPR survey as the swallow flies, slightly further as the archaeologist trundles.

The GPR team were not to be outdone by the mag team.  Here are four time slices from the area they did today. Remember each slice is going a bit deeper into the ground.

Day 31, GPR slice 2 (9.5 to 12.5ns).

Day 31, GPR slice 2 (9.5 to 12.5ns).

Day 31, GPR slice 3 (12.5 to 15.5ns).

Day 31, GPR slice 3 (12.5 to 15.5ns).

Day 31, GPR slice 4 (15.5 to 18.5ns).

Day 31, GPR slice 4 (15.5 to 18.5ns).

Day 31, GPR slice 5 (18.5 to 21.5ns).

Day 31, GPR slice 5 (18.5 to 21.5ns).

The top image (time slice two) is just showing noise in the ploughsoil.  The second image is showing a nice Roman building very clearly.  There might be more than one phase, with the upper phase being somewhat damaged.  The third image shows the building very clearly.  In the last image some of the internal walls show a little more clearly suggesting that they may have been robbed or replaced at some point.  All in all, a rather nice building in a prime position on the road across the town.

The GPR team have now covered quite a large area of the town!  Remember that they have to walk four times the distance to cover the same area as the mag, but have the advantage of being able to create images at different depths.

The extent of the GPR survey after day 31.

The extent of the GPR survey after day 31.

The Earth Resistance survey managed four grid squares today after the rain made it possible to take readings at all!

The earth resistance survey after day 31.

The earth resistance survey after day 31.

The res has picked up some more details of the Insula XVI temple.  Unfortunately, the trick of spreading the remote probes widely apart to avoid problems with grid matching has finally failed.  We did not have enough rain to change the moisture levels at 50–75cm down, so I am not entirely sure why this is the case.  Perhaps some current leaks through the grass?  I’ll have to investigate.

The weather forecast is better for tomorrow and so we will be out again in force.