Tag Archives: Roman

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.

Watling Street

Firstly, apologies to those who turned-up and found themselves unemployed. With ground conditions difficult for the resistance meter, we just couldn’t run all three machines. Thank you for being so understanding.  Looks like it will rain most of tomorrow, so hopefully we can press-on with the resistance survey on Saturday.

The mag survey in the second field, which I am going to call the macellum field for convenience (it isn’t the field’s real name) is going well.  Firstly, an image of the whole town:

The mag survey of Verulamium.

The mag survey of Verulamium.

My long-held dream of having a complete survey of Verulamium is getting close to becoming a reality!  Thank you everyone.

Looking at the new area in more detail:

The area surveyed on days 29 and 30 in the macellum field.

The area surveyed on days 29 and 30 in the macellum field.

Hopefully, everyone can see the clear linear feature running from the SE to the NW.  This is Watling Street, the main road from London to Chester.  As one might expect just near to the gate (which was robbed and then excavated, and lies in the trees), there appear to be lots of little buildings along the road which show as white lines against the mid-grey background. What is more curious is the rather different look of that background: much less even and more noisy. I’m not sure why, yet.  The field certainly feels different: flatter, slightly different vegetation, and is obviously closer to the river.  Perhaps we have moved from chalk to the river gravels?  I must check the geology map…

The GPR has been doing lots of bitty blocks around the edge of last year’s survey area.  Rather than hold-up the posting of the mag data, I thought I would do the GPR later when I have dropped all the different areas on to Google Earth.

Thanks to everyone who helped today, especially Graeme for acting as my driver and go-fer as I limped around the field  (don’t ask!), and Ruth for helping transport all the equipment.

 

Around the bend

We are within four grid squares of completing the “Theatre Field.” The sheer size of the field doesn’t really come across in the images. From the northernmost point to the southernmost it is 855m and it is 600m from east to west, enclosing an area of 27ha. That is about 38 soccer pitches in area!

The survey of the Theatre Field after day 28.

The survey of the Theatre Field after day 28.

But enough of all this nonsense about soccer pitches, I hear you cry, what about “the sinuous ditch”?  Well, here it is…

The course of "the sinuous ditch" after day 28.

The course of “the sinuous ditch” after day 28.

Yup, the ditch is now heading north again.  On a flat image, this looks really odd but when one is in the field it seems pretty clear that it is following the contour lines.  Perhaps we can still consider the ditch an aqueduct?  Here is a detail:

Detail of the area at the end of the sinuous ditch.

Detail of the area at the end of the sinuous ditch.

The section of the ditch surveyed today seems very broad, and gets a bit fuzzy near the big irregular feature shown in stronger black and white.  My guess is that the irregular feature is a later quarry pit — very common in the Hertfordshire countryside — and this may have partly destroyed the ditch.  Who knew that the last four squares might provide the answer to this mystery feature!  There are also quite a few weaker and more indistinct ditches in this area, along with quite a few pits.

The GPR crew worked their way steadily eastwards along the northern edge of the Theatre Field.  They have covered an amazing area too.  Remember that (a) they have to walk four times as far to cover the same area as the magnetometer and (b) their cart is dragging a plastic tray along the ground.  In longer grass it is quite a difficult task.  Despite this, look what they have now covered.

The total area covered by the GPR.

The total area covered by the GPR.

This image is a bit of a mish-mash of different time slices but it conveys the main message… look what we have covered!

Here is a detail of the last two days area:

Detail of the area covered during day 27 and 28 of the survey. Fourth time slice (15.5 to 18.5ns).

Detail of the area covered during day 27 and 28 of the survey. Fourth time slice (15.5 to 18.5ns).

The surviving wall foundations are easy to spot: the black lines looking like buildings!  We are, however, also seeing the outlines of building foundations in white where the stone has all been removed just leaving robber trenches.

The GPR data is just being fairly crudely processed here as it takes much longer to do than mag or resistance data.  At some point I will need to process it all in much more detail and much more consistently.  It does, however, give us an excellent comparison with the mag and res data even with this basic level of processing.

Tomorrow and Tuesday are our “weekend”.  We all deserve a rest!  Many thanks to everyone, I hope you agree it is worth the effort.

Two days work

A quick posting to show the results from yesterday and today. Firstly, the magnetometry:

The survey of the Theatre field after day 26.

The survey of the Theatre field after day 26.

As can be seen, we are slowly getting close to completing this huge field.  Looking in more detail at the area we have surveyed over the last two days:

Detail of the area surveyed over the last two days.

Detail of the area surveyed over the last two days.

As can be seen, we have finally “turned the corner” and completed the survey of this section of the “1955 ditch”.  It is interesting to see that the corner seems a bit odd.  Was it filled in quickly?  Was it never completed?  There certainly seems to be a bit of a break in it.  Outside the ditch to the north is… well, not a lot.  This area is, however, quite a steep slope down into the valley in which the infamous “sinuous ditch” runs.  Unfortunately for the mag team, we had another sensor freeze and we will have to re-do part of one grid square just about on the steepest slope.

The earth resistance survey has been progressing slowly.  The hot weather has led to dry conditions in the top few centimeters making it hard to survey with the res.  We have, however, started to pick up the temple very clearly.

The earth resistance survey after day 26.

The earth resistance survey after day 26.

The earth resistance survey after day 26 with a high-pass filter applied.

The earth resistance survey after day 26 with a high-pass filter applied.

Lastly, the GPR results.  I have only processed yesterday’s survey so far, but the team have found another couple of buildings:

GPR survey from day 25 (top block), third slice (12.5 to 15.5 ns).

GPR survey from day 25 (top block), third slice (12.5 to 15.5 ns).

The plough soil up against Gorhambury Drive is probably quite deep judging by the depth of the road so I am surprised we are still picking-up buildings so close to it.

That is all for tonight.  Many thanks to everyone who toiled in the hot sunshine.  It is most appreciated.