Tag Archives: Arts and Humanties Research Council

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…!

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.

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.

A hot and sunny day in the Park

After the cold and rain of the previous day’s survey, today was a scorcher!  Burcu Urundul (Welwyn Archaeological Society), John Dent (St Albans and Herts Archaeological and Architectural Society) and Ralph Potter (West Essex Archaeological Group) were out today continuing our survey in Verulamium Park.  There was a minor hiccup at the start of the day when a toddler wandered off with the pin flag we were using as a backsight for the Total Station!

Survey in the Park

Burcu and John surveying in the park.

We did, however, manage to survey another five 40 x 40m grids.  The results are posted below and are very interesting.  The ‘1955’ ditch clearly shows across the plot, and there are a number of ditches and linear features.  One feature that catches my eye is the rectangular one indicated by the white arrow.  It is about 4.5m long and 2.75m wide and is quite strongly magnetic at about 12 to 20 nT, but not so much so as to be metallic.  Very curious indeed.  It is also interesting to see that there appears to be more activity inside the ‘1955’ ditch (to the NE of the plot) than outside it (to the SW).

day3results

The results of the survey after the third day.

Tomorrow sees us out for the last time before next weeks course.  Wish us luck!