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Volunteering on the Caerleon Excavations 2011 – Trench One

September 12, 2011

During the summer of 2010, Cardiff University continued with a large scale excavation within the legionary fortress of Caerleon. This was part of the Priory Field Excavations 2007-2010. While there, as part of their under-graduate degree, the students undertook a huge geophysical survey of the fields to the south of the amphitheatre. This produced quite remarkable results and the resulting interpretation of the survey shows a monumental complex lying next to the river Usk.

How the fortress and port may have looked like in AD74

Those of you that have visited the amphitheatre at Caerleon will be able to recognise the sheer scale of the construction - It dwarves it in comparison.

This exciting discovery was released to the press in August 2010 as test pits in the area were being excavated. One  of the test pits was placed quite close to the river Usk and it threw up a wall built entirely of tegula. These are roof tiles and when used in conjunction with imbrices they formed a durable  and waterproof roof covering.

Each tegula (a) overlaps the one below it and its raised lateral borders tapering in to nestle between its lower tile's upper border. Each curved imbrix (b) covers the side ridges of the joints formed between adjacent tegulae. Some imbrices are not shown in order to reveal the details of the tegular joints.

So why on earth were they used during wall construction? Obviously they are waterproof so they would be ideal for a port but the port excavated in Caerleon by Boon in the late 60’s produced walls built entirely out of masonry. A comparable  had to be found. Dr Peter Guest found that the port walls in Ostia – Harbour City of Ancient Rome were built of the same Ceramic Building Material (CBM) and armed with this information he approached CADW with a plan for nine evaluation trenches during this summer. The laying out of the trenches was undertaken by Tim Young of Geoarch and he blogged his activities for The Day of Archaeology 2011.

© Geoarch

As you can see, most of the trenches were of the same size. Two metres wide and twenty metres long. Only two were different, trench one and trench three. Evaluation trenches are just that, they are there to evaluate what the archaeological remains could be. It is minimum invasion for maximum information. As it was already thought what was known in the area of trench one, permission was granted for a larger area to be evaluated. Trench three had the same area to be excavated as the rest of the trenches, forty square metres, but the shape was different at ten metres by four. After a brief spell in trench five, it was trench one that I ended up in.

The wall had already been re-exposed by the time I got there. The photograph to the right is facing an easterly direction. The right hand side of the photograph is near to the Usk and the test pit excavated in 2010 can be seen at the bottom.  As the trench was widened the tegula wall majestically extended across the width of the excavated area. For some reason the Roman engineers had built the wall slightly wider than the width of the actual tile. To do this, each tile was roughly split down the middle and then each course was laid down using clay mortar – thus ensuring a water tight barrier.

One of the first questions that I asked myself was why construct the wall wider than the tiles? The tiles could quite easily have been moulded in a different size. Judging by the scratch marks on the back of each tile the moulds were probably made of timber and as such, easily made or easily altered. That not being the case there must have been another reason why these tiles were used and the answer may lie in the fact that they were mass produced. Is it possible that these tiles were the result of surplus production? It would certainly fit in with the amount of CBM used as walling found in other trenches around the site. If that is correct, how on earth did the Roman military machine, normally so efficient when it comes to construction, allow so much surplus material to be manufactured?

I could probably give umpteen reasons for the use of this material ranging from it being easier to use construction wise, to the tiles being seconds or broken during the manufacturing process. Each theory would be hard to argue against.

That is not the end of this particular story in trench one. On they went, deeper and deeper to try and get a further understanding of the archaeology.

This is the eastern side of trench looking towards the Usk. Interestingly a river cobble foundation was used to support the riverside wall.

Looking from the Usk side at the same wall you may notice a dark staining of soil right next to the wall. This is probably the remains of timber, possible used as part of a jetty projecting out into the Usk. This development would give us a direct parallel to Boons excavation of his third century port lying to the west of the amphitheatre.

All in all this trench was fascinating to watch as it developed over the weeks of excavating. I haven’t revealed all of its secrets, some of which I found quite surprising. Other areas of the trench threw up some quite surprising archaeology, not least because the geophysical survey had not revealed it.

Now that was fun.



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  1. The Fortress Baths at Isca « monasticdave

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