#ThrowbackThursday – Colchester Sixth Form College

This #ThrowbackThursday we are learning about one of the most prominent features in Colchester’s heritage – its huge and imposing Roman wall! CAT knows a great deal about it, but new excavations enable us to learn even more about its date and construction

A perfect example of this was during an excavation in the summer of 2005 ahead of new building work at Colchester Sixth Form College. In order to build a sewer for the new development, a trench needed to be cut through the Roman wall. Disturbing such a cherished national monument can be fraught with problems, but CAT saw it as a golden opportunity to find out exactly how old the wall was

As predicted by our very own Philip Crummy, the excavation of the wall’s foundations found vertical timber piles plunged into the ground, with the foundations intentionally flooded with groundwater before being sealed with a layer of sand and gravel. The base of the wall was then constructed from a combination of septaria and opus signinum (waterproof Roman mortar). Does this construction technique have any parallels? Yes – and it is extremely close! In fact, the foundations of a Roman bath house beneath the Sixth Form College was also deliberately flooded, with wooden pipes found below the structure’s floor. The Romans certainly knew what they were doing, and developers were astonished by how they used similar techniques today! The fact that it still stands today, amidst a long and violent history of sieges, battles and even an earthquake, just demonstrates the genius of Roman engineering!

So what about the dating of the wall? Crucially, a large quantity of pot-sherds were recovered, indicating that the wall was first built in the early 1st century AD – possibly following the destruction of the Boudiccan revolt – and then subject to strengthening about 300-400 years later. Our excavations tried to go further than this using dendrochronology, which measured the annual rings to establish not just a rough idea of the century the wall was constructed, but the precise year that the tree was chopped down!

Unfortunately the timber at this site was not preserved enough for accurate dating, but hopefully with the development of better technology and the discovery of new sites we will be able to put this extraordinary technique to good use!

For more information, check out the CAT report here: http://cat.essex.ac.uk/reports/MAG-report-0019.pdf

Written by work experience student Alex