 Thank you very much and it's lovely to see so many people here. So my talk today is basically going to have three sections. First of all I'm going to introduce the project and how it came about. I'm then going to give a very brief overview of the geophysical survey techniques that we use just so that everybody understands what the funny looking maps are in the third part, which is the investigation of Feroleynium. So four years ago the Arts and Humanities Research Council, through a thing they call their Connected Communities Scheme, had a grant scheme for something they called a jointly authored research project. This was a research project which wasn't coming from somebody at the universities, wasn't coming from community groups, but was something that came out of both those groups working together. Now, as Christia said, I've worn two hats for many years, being director of the Welling Archaeological Society for the last few years, and also being an academic at UCL. And through that I knew that local societies had various interests, one of which was undertaking geophysical survey. And here's the Welling Archaeological Society undertaking what's called an earth resistance survey at a site, Mildlybury, near Dachworth. The problem that most local societies have with geophysics is that they nearly always do earth resistance survey. And they do earth resistance survey for one reason, and that it's the cheapest of the geophysical survey techniques. It's not very quick. It's very badly affected by changes in the weather. You'll get quite different results if you survey in the middle of summer and if you survey in the middle of winter. And as a result, I didn't necessarily get the best of results. In the commercial world, the first technique that any commercial geophysicist would use is technical magnetometry. But for most local groups, magnetometry was out of their price range. They just simply couldn't afford the machinery. So my idea was that perhaps we could set up a group which was an umbrella over local societies that trained them how to use magnetometer, supplied them with a magnetometer, and then went round undertaking surveys on a variety of different sites. So I emailed round the various societies and museums, the county archaeologists, the HGR with this suggestion to see whether people thought it was a good idea. And everybody really liked this idea, so I'll put the application in, and lo and behold, we got the money. That paid for us to buy a machine. It paid for the search assistant for a year, part-time search assistant for a year, and it paid for a course in geophysics that we ran for a week in the summer of 2013. So here you can see a list of the groups that are now involved in this project. All of them are on board right from the beginning. And out of that initial year's funding has grown something that we have called the Community Archaeology Geophysics Group. You can see our logo up in the corner there. And we handed out some cards at the beginning of that. So although that group was only funded for a year, we have now been out surveying for the last four years. So really, this lecture ought to have all of those people's names on the front of it. Only Chris would be here for a very long time if you had to read all those out. It is very much a community enterprise. It is reliant on all of these people from all of those different societies for the work to actually happen. And really, it's the enthusiasm of all those people that drives this project on. So we ran a geophysics course in Verlanium Park, perfect place to run a geophysics course. We have the museum to give lectures in the morning and then 80 acres of archaeological site to go out and practice in the afternoon. And here we can see an earth-resistant survey, a ground penetrating radar survey, and a magnetic susceptibility survey. It was great fun. The mayor of St Albans, as it then was, came down to visitors. I'm not quite certain what all this tat round her neck would do to our mangotometer. But it was some welcome publicity. That course, however, was the cherry on the cake, really. The meat of the project was buying a magnetometer and going out and doing these surveys. The magnetometer we decided to buy is this machine made by a German company called Forster. It's not designed for archaeology. The manual for it says your partner in UXO detection. This is a bomb detector, and the UK rep said they've sold about 400 of machines in Britain, five to archaeologists and 395 to people who go and find mines and unexploded bombs and stuff. For us, it has lots of advantages. One of the advantages is that it has four magnetic sensors, and I'll go into that in a bit more detail in a minute, which means that it's quite quick. We survey in two-metre-wide swathes backwards and forwards across the site. It means that people of widely varying ages, statues and health can operate the thing. You don't have to be able to trot at the particular speed. It doesn't matter if you're short or tall. The other thing is that most of the machines on the market rely on a sort of metronome system to measure distance. This machine has an odometer here. It measures distance. You start the machine on a baseline, you walk along your screen, and when you get to the other end, it automatically turns itself off. It doesn't matter if you walk slightly slowly or slightly quickly. It will measure the distance for you. For our purposes, it was an ideal machine. This chap here is my friend, Jared Burks from Ohio, who uses one of these machines commercially. He was very kind to come over for the geophysics course and train us on how to use it. Over the four years the project has run, we have now surveyed on 21 sites. This is 20 of them. The 21st site is Dura Breivai, Walter Newton up near Peterborough. If I include that, the map gets so small that I can't see the rest of them. As you can see, as originally intended, most of the surveys are in Hartfordshire, but we have ventured over the border into Essex, Cymru, Bedfordshire, up into Cambridgeshire, and even one survey not very far from here on Primrose Hill last February. The technique that we were planning to use on all of our sites is this technique called magnetometry. Unsurprisingly, we are measuring magnetism, and we have four sensors that are measuring the magnetic field. We are collecting four lines of data at any one time. As you push the machine along, it is collecting a reading every 10 centimetres. We are collecting 20 readings per square metre, a very high data density. Why do we care about magnetism? Certain things are magnetic, so anything ferrous is magnetic. Unfortunately, most of the ferrous things we find are not what we are interested in, so horseshoots, tractor bolts, old water pipes, that sort of thing. It's also very good at finding things which are burned, particularly burnt clay. If you heat clay to a high enough temperature, the iron particles align on the earth's magnetic field, and when it cools down, that clay will be slightly magnetic. A house brick, for example, is a very weak magnet. I won't try sticking it on the fridge door, you'll end up with sore toe. But it is, we can find it. The rotting organics are also slightly magnetic. Very faintly magnetic, and we wouldn't be able to see them unless you put them in a giant magnetic field. Luckily, the earth generates a giant magnetic field, so we can see these organic remains as well. So anything archaeologically, which is either burned, like a kiln, or half, or has a negative feature, like a ditch or pit, that takes this organic material, so you have a concentration of it, will be able to see it with the magnetometer. So it's very good for ditches and pits and kilns, but normally you wouldn't be able to see something like a flint wall, which in Hertfordshire is quite important, most walls are made of flint. The other problem with the earth's magnetic field, however, is that it isn't stable, it's always varying. So in fact, as we're pushing this machine along, each time the machine takes a reading, it takes a pair of readings, one at the top of the tube and one at the bottom of the tube, and simply by subtracting one from the other, we get rid of the problem of the planet. Just to show you more planet's problems can't be got rid of so simply. We can get rid of the problem of the planet just by subtracting one from the other. And when we plot the results of a magnetometry survey, this is what they look like. So a sort of mid grey is our zero, is our background noise. Black is a very strong positive reading, white is a very strong negative magnetic reason. You know that a magnet has a positive and a negative pole. So when you see something which is a strong black and white line, like these, those are the classic signature of an old water pipe under the ground, or perhaps an old fence line or something like that. Usually not something we're interested in. Most of the other features you see on this thing are ditches and pits which are filled with magnetic material. So the bits that looks like somebody's thrown a plate of spaghetti at the field, that's an iron age settlement. We can date it from the fines on the surface. And then the more regular field systems up the top here are part of a small Roman settlement with a road running through the middle. On top of that, we have these curved lines, and those lines are a survival of the region furrow cultivation system that despite modern plowing still is showing in the subsoil and still can be picked up with our magnetometry survey. So that's how we read a magnetic plot. Mid grey, nothing very interesting, black and white delineating the features that we're looking for. The other technique which we use regularly is the one I've already mentioned, Earth Resistance Survey. And with the Earth Resistance Survey you have two probes on a frame, two probes on the end of a long cable, and you pass an electric current from one probe to the other probe through the soil back through the cable to give a circuit. And the reason we do this is if you have something under the ground which is solid and dry, the current won't pass so easily so you get a high resistance. Whereas if you have something under the ground like a ditch or pit that holds water, pulls water, the current will flow more easily and will get a low resistance. So by plotting high resistance and low resistance features on a map we should be able to see walls and if we're lucky be able to see ditches and pits. Tends to be better at the solid things than the negative things. The reason we have four probes is simply that you can't measure the resistance with the same current that you're passing the electric through. So you have another circuit which measures the electric, the voltage potential to do that. That's our four probes. Those of you with sharp eyes will notice that this machine, our nice new shiny one which we only got last summer actually has a fifth probe. And that's simply to speed up this very slow technique. So when you stick it in the ground it takes one reading, swaps to the other machine, takes a reading and then swaps back. So as we move along it's taking two readings side by side just to speed the survey up. And this is what an earth resistance survey looks like. This is at Durabrivi up near Peterborough and the square building in the middle there or two squares one inside the other is the classic signature of what we call a Romano Celtic temple. Very distinctive building form. Why is it showing as low resistance? Well in this particular case the foundations of the building in between the foundation walls is full of very fine silt with not very much in the way of rubble. And as a result it's holding moisture so we're getting a low resistance feature. Along here the high resistance features are showing as walls, bits of road or a very big rubble spread. Up here where a big public building was demolished. The last technique that we have been able to use thanks to an organisation called SIHA if I can remember what it stands for Science and Engineering in Archaeology, Heritage in the Arts. It's a doctoral training school jointly between Oxford, UCL and Brighton. We've been able to borrow their ground penetrating radar. And this fires a radar signal into the ground which as it goes through the ground and hits something solid bounces back and is received by the antenna. It's basically exactly the same thing as people use to find aircraft in the sky. It's just we're pointing the radar being directly into the ground rather than firing it up into the sky. Because of the way it's working our original set of data is a vertical slice through the ground. A long thin vertical slice of transect across the ground. So it's one of the few techniques that immediately gives you a sense of the depth of different features. Unfortunately, those vertical slices are a bit hard to read and it's taken me a long time to get my head round these. But essentially when it hits something hard you get essentially an echo. So here is the top of a wall and you can see the echo down below. And then some of the signal goes through the wall and when it hits the bottom of the wall trench and the saw going changes from the material the wall is built of to the sub-saw you get a second echo. So we've got the top of the wall and the bottom of the wall. Now other things will also cause echoes. So if you'll notice I've labelled on this slide something called wing which is right near the surface. And one of the things that will cause echoes is water. And one of the things that holds water are mushroom rings. So we get a beautiful map of the mushroom rings at Gormbury. Of course most people really don't want to look at plans like that. They send you across side and give you a slight headache. But what we can do is stack them side by side and slice them in the other direction. So that you can turn those vertical slices into a plan. So here we have just one block of GPR data from Valenium which shows quite nicely a road. A series of buildings, there's one here. A courtyard, a more ephemeral building in the back another building in the back and so on. So we can get a plan of structures using GPR. Again it tends to be much better at picking up solid things like walls and roads rather than negative features like ditches and pits. And here's just a comparison of exactly the same plot of landscape at Dura Brivai where we can see the patch marks in Google Earth and then I've overlaying the Earth Resistance Survey that you've already seen, the Ground Penetrating Radar Survey and the Magnetic Survey. And you'll notice that the temple just doesn't show in the Magnetic Survey but what it does show is that either side of that temple are large pits full or burnt organic remains. So we've got the building and then we've got pits either side of that temple. So one of the things, if you have the luxury when the group started off with one machine and we've now got access at least to three machines if you have the luxury of both time and equipment doing more than one sort of survey will give you a much richer picture of what's under the ground than simply doing the one survey. If you rely just on magnetometry you wouldn't know that temple was there but it does show in both the Resistance and the GPR Surveys. So now to move on to Vorolanium. Vorolanium, the Roman town of Vorolanium at St Albans in Hertfordshire is now under, half of it is part of the public park so that the near side of this photograph is a public park the far side of it is part of the Earl of Rherom's estate the Goronbury estate. The blue line that runs through the middle is the line of the now main road from St Albans to Hemel Hempstead but it was the line of a narrow lane in the 1950s Blue House Hill. The red line on this image represents the third century town wall which mostly survives under a bank covered in trees and a short section of it was excavated by some Aldermawila. The theatre which I've marked there was excavated by Kathleen Kenyon in the 1930s and most of the public buildings are in that central area underneath the older village, the church, the rectory, the museum, the museum car park and in fact the public buildings are very difficult to access. So why do we care about Rherolanium? Well, Rherolanium is the third biggest Roman town in Britain after London and Sir Ancestor. It's about 81 hectares. Most of the public towns in Britain have a modern town built on top of them for them don't, Roxeter, Silchester, Rherolanium and Keisterbyn Norwich but Rherolanium is the biggest of those four towns that are available for this sort of survey work and until we did our work it was the only one of those four towns which hadn't been completely surveyed. Roxeter had been done in the late 90s, Silchester and Keisterbyn Norwich more recently but Rherolanium hadn't undertaken this complete survey. We do know quite a bit about Rherolanium however because a few famous figures in British Archaeology Mortimer and Tessa Wheeler, dug there in the 1930s when the area which became the park was given to St Albans Council. They invited Mortimer and Tessa, it was knighted later to come and excavate and he excavated really quite a large area of the park. And then in the 1950s into the early 60s when Blue House Hill was upgraded from a small country lane to the main road to Hemel Hempstead Shepard Freyr excavated along the line of that road. Rherolanium was also the site of the second ever magnetometry survey in archaeology. So the man sitting there with the machine is Martin Aitkin who was in Oxford at the time and this machine you had to set it up on a tripod, adjust it, point the arrow towards north, take a reading, move it, adjust it, take some. He was very pleased that it was a quick technique that he managed to collect 3,500 readings over two summer seasons. I think with our machine we collect 3,500 readings about every ten minutes. But having said that, he did trace the line of the first century boundary of Rherolanium a feature which we now call the 1955 ditch. Not because it was dug in 1955 clearly but because Shepard Freyr dug a section across it in 1955 and the name stuck. The young lady here is actually Rosalyn Niblid who many years later became the district archaeologist for the Sinoordyns and is one of the main authors writing about the Roman town of Rherolanium. So here's the town. We have Watling Street, the main road from London to the north west running through the town. We have this thing, the 1955 ditch which we know from that early geophysical survey. The theatre dug by Kathleen Kenyon in the early 30s. The former Basilica that we don't know as much as we'd like to know about because it's underneath the church and the church yard and the rectory and so on. We have the third century boundary of the town, the town wall and then this area where the wheeler is excavated in the 1930s and Freyr excavated in the 1960s. But you'll notice from this map that there's an awful lot of open spaces and that's what we were hoping to fill in with our surveys. So here is our survey at the end of three seasons worth of work. We surveyed on and off throughout 2013 and then we've done two summer seasons in 2015 and 2016. That represents 81 survey days, almost 13 million data points and just walking backwards and forwards up the stream so not getting from the car to where the grid square is or laying the grid square on it or any of that is 322 kilometres of walking, pushing that machine backwards and forwards. For the last two summers we've had access to ground penetrating radar and here's the radar results, 8.5 hectares of radar largely almost entirely at Gorombrae side of the town. And then last summer my employees bought a nice new shiny resistance meter and we managed to do two and a half hectares of earth resistance survey as well. Now obviously at this scale it's really difficult to see what's going on. A few things stand out. Now I said earlier that a bright black and white line like that is probably a water pipe, something of that sort. In this case this isn't a water pipe but a male of it, that signal is about 30 metres across. This is a 12 inch gas main put in in the 1950s which is about to be relined. But to pull out some of the results of what we've been doing I'm going to zoom in on some of the features and look at different classes of structure. So to start with I want to think about public buildings. And on the whole most of the public buildings are not accessible to geophysical survey because there's a church and a graveyard on top of that and so on. But one of the public buildings is available and that's the temple in incident 16. It's here on the overall magnetometry plot. You can see the details of it here. And this is the published plan in one of the books about Rheolania. One of the things which is interesting about that published plan is you'll see it reproduced in all sorts of guidebooks on Roman Britain and so on. But Rosalie Niblitt went back to the archive and looked at how much of the villa the temple had actually been excavated. And the bits in the red lines are the actual excavation trenches. So an awful lot of the plan of that temple is actually join the dots. We've got a bit here, we've got a bit there. They must be straight lines because they're Romans after all. And we can reconstruct the plan of the temple. Looking at our various geophysical survey results we can see that we do indeed have these triple walls around the outside particularly in the grand penetrating radar survey here, you can see the triple walls. We have a little bit more detail of the keller. This seems to be a little separate room at the back rather than something joined on shown here. The resistance and the GPR survey show very nicely the strip buildings along the side of the road. And there seems to be a big pit here full of burnt material. Now whether this is a pit that is related to the temple or whether it's something that happens later we can't say just on the basis of the geophysics but there certainly seems to be some sort of big burnt feature there. So by combining those three surveys we get a better idea of what is surviving of the temple and of its plan. One of the other structures I should say in the town is this thing that we call the sinuous ditch. Now when we first started surveying at Gombray and started finding this ditch running across the site we were a bit puzzled as to what this thing might be. There were various suggestions and speculations but the interpretation of it is easier if you compare it to an old late 19th century ornate survey map which happens to have the 300 foot contour on it. And you'll notice that our sinuous ditch follows the 300 foot contour almost exactly. The only interpretation of it that seems to make any sense to us is that what we have found is the town's aqueduct. Upstream near Redbourne there's a leat coming off the river Le and then the channel has been very carefully graded so that by the time you get to Rowlanium the water level in the aqueduct is 20 feet or so higher than the river which gives you water pressure for ffanteins and so on downslope along Watling Street. This is Watling Street here running along. So we have the advantage of the height to give us water pressure for things downslope from the... One of the things that we noticed towards the end of the aqueduct is normally as I said the stone building shows black lines so here we have a nice stone building but if the stone building has been substantially robbed what we'll get is the opposite we'll get a white line, we'll get an absence of reflections and you can see white lines here with a solid block in the middle which is probably a floor and what we seem to have here is a structure where the walls have been quite badly robbed so we have a building with substantial walls worth robbing at the end of an aqueduct next to the theatre and upslope from where in the 19th century they found drains that ran down to the river Ver I guess that we have finally found Verolanian's public baths Again it's an interpretation and we would have to dig a hole to prove that but it seems the most likely interpretation of that result at the moment. As well as public buildings there's evidence for a number of private buildings and I've just picked one of these out we jokingly call this the motorway service station because this is Watling Street running up to the Chestergate and here is this big building that I've circled here one of the curious things though is these buildings are made of flint so we shouldn't be able to see them in magnetometry data but what's happening here is that because they have dug a hole in the slightly magnetic soil and replaced it with non-magnetic flint and we set our zero point to be that background magnetism it shows as a negative feature so the stone walls often at Verolanium show as white lines Of course if it's flint which isn't magnetic you're not going to get a negative and a positive end of a magnet so if you find as we do here that you have higher magnetism in between those walls that is some sort of tiled floor some sort of fired floor rather than just the negative and positive end of a magnet Now this building had been known previously been seen in aerial photographs this one is from the frontispiece of Sheppard Ffair's excavation report there's a detail of it and we can compare various aerial photographs with a plan derived from them which is published in the late 70s one of the things I'm trying to track down is that in 78 they dug a small trench across this building and it would be quite good to be able to get the section drawings and the finds and so on to compare with our survey results As well as big rather swish buildings like that we have areas of the town where there are lots of much smaller structures so here we have a crossroads and you can see lots of smaller buildings of the road probably workshops more modest dwellings shops, that sort of thing nestling around this particular crossroads in the town The magnetometry park gives quite a lot of detail the ground penetrating radar map shows the road very nicely and these buildings and the small internal rooms and so on and the truck buildings in the courtyard at the back and even the earth resistance survey that I was so moved about at the start of this lecture shows the road and these structures and then this is another road this is the other road running at right angles to it with more buildings another building with a small room inside and so on so again we're beginning to pick up beginning to be able to put together a plan of the town where the big buildings are where the small buildings are there's a certain amount of industry at Verlanium Verlanium was very well known for having a pottery industry a number of kilns were excavated south of the town in the 1960s in the magnetometry survey from the southern part of the town there are some very clear pottery kilns in the data so very strongly magnetic features with this sort of very distinctive shape we can see a small stone building here a ditch probably another pottery kiln and I think in this some bit of the town we have a little potter's workshop we do have a problem though that there are quite a lot of kilns and sometimes they're very obviously kilns like these ones here other times it's a bit more difficult to tell whether the feature is a kiln or not so A here is that a kiln? maybe, maybe not this one up here is that a kiln? maybe, maybe not and so what I did is I looked at the readings that we've got as we went across kilns that we knew were kilns and worked out what the lowest and the highest values were we measured magnetism in things called nanoteslas so for each feature worked out the lowest, the highest and then the range and then if we look at kilns that were happier pottery kilns we can see that the range of them is between about 128 about 183 if we look at the two I wasn't certain about A is right in the middle of that range so I think we can be fairly confident that that is another pottery kiln whereas E, the one which was over to the eastern side of the plot is well over twice that range and is probably a couple of old horseshoes or tractor bolts or something like that it's more likely to be something ferrous I was very pleased with A that I went back to look at the GIS for the town discovered that there was a building right next to A looked up that building it was building instead of five building three excavated by the wheelers in the back of the building the wheelers had excavated pit six and pit six was full of killed wasters and kiln furniture pottery wasters and kiln furniture so I think we can be fairly sure that A is another pottery kiln what about boundaries of the town well we know about the first century boundary this thing called the 1955 ditch we know about the third century boundary the town wall what happens in between well if we look at the southern part of the town here are those two boundaries you'll notice that this area is very empty there's very little going on there this area however where pottery kilns are where Watling Street is and various other buildings and so on is very very busy and between the two there is another ditch and I suspect that this ditch is at some point between 8080 when they built the first ditch and some point in the third century when they built the town wall they decided to incorporate this busy and popular suburb into the town boundary in order that they could tax them probably and that this ditch probably represents that extension sometime in the second century maybe again we could only prove that well we could never prove it but we could add to the probability of that interpretation we could put a tiny little trench across there at some date and get some dating evidence out of it so where do we go from now well this is the public buildings in the middle of the town this is the area where we largely get rich wealthy mosaic buildings the big town houses in the second and third centuries we get areas with much smaller much more modest housing we get an industrial area and we've got an area which has very little going on and would seem to be largely some sort of agricultural area that was incorporated within the third century boundary when they expanded the town so that's a working model of how the the town plan develops we've got all sorts of things we have to do it would be nice to go on and do some more survey particularly the ground penetrating radar survey I've only looked at it in a very superficial way it's very complex data and something that before I started this I didn't have much experience on so I've got a lot of work to do going through all the numbers for that obviously we need to publish this job interpretation plans and so on but also it's nice knowing about Berlin didn't tell us very much unless we think about other Roman towns and whether those Roman towns are in Britain or whether those Roman towns are somewhere else in the empire now quite a few towns in Italy and Spain as well as the ones in Britain as one in Austria and so on where we have these sorts of large-scale geophysical surveys what do these large-scale geophysical two surveys tell us about urbanism in the Roman world and we need to pull those sorts of things together in the more immediate future we want to do some more survey we've done a little bit of survey with the ground penetrating radar on Virlane and Park last November but we are going to carry on surveying Abbey Orchard the day after tomorrow I've just got permission a couple of weeks ago to survey this one last remaining open area within the town walls at Daraffield House in March and then hopefully hopefully in August we'll be able to extend the surveys particularly the ground penetrating radar and earth resistance surveys in the Gormbury estate next August the last thing I wanted to say is just to remind you that all of this work would not have been possible hadn't been for this wonderful group of people who turn out at all sorts of times of year all sorts of odd places around Hertfordshire all sorts of weather and push these machines backwards and forwards and collect data and it's their enthusiasm and their hard work as much fun as it is thank you very much