When the Romans invaded in AD 43, Colchester - or CAMVLODVNVM - was the most important and powerful Iron Age settlement in Britain. It had been ruled by one of the early kings of Britain, Cunobelin, from 5 BC to AD 40.

For the invasion force, the capture of Camulodunum was an essential first step in subduing the new province. A large site, covering an area of thirty two square kilometres, it was protected by a series of massive banks and ditches which are still visible today. But the Romans, with their well-organised legions, easily captured the settlement, no doubt helped by the elephants they had brought with them to terrify the locals.

The Romans made Camulodunum their capital for the first few years of the occupation, before moving it to London. A legionary fortress was built here, on the site of what is now the modern town centre. We know from Tacitus and Suetonius that a large classical temple was built and dedicated to the Emperor Claudius in Colchester, to celebrate his great victory. In the 1920s excavations by Mortimer Wheeler in the vaults of the Norman Castle in Colchester revealed that these were in fact the original vaults and foundations of a huge, classical temple. It is now accepted that these vaults under the castle were the original Roman foundations for the Temple of Claudius. These vaults can still be visited, by arrangement with the Castle Museum.

In AD 60, Boudicca and her army attacked Colchester,in particular the Temple of Claudius, which was to them a symbol of the Romans' oppression. The Roman colonists and their collaborators took refuge in the Temple, but this didn't save them. They were massacred by Boudicca's hordes, who burnt the city to the ground.