When the Romans invaded Britain, they monopolised native strongholds. As time passed, they built base camps that allowed their armies to travel safely through the country. At first they fortified these camps with timber, then from the second century CE they used stone. The Romans were expert builders and had perfected the art of masonry by creating a revolutionary new material that was known as ‘opus caementicium’ – a concrete made of rock, rubble or ceramic tiles. Walls were built by placing mortar and stone in large wooden frames, and the result was a facing that has endured centuries. Opus caementicium was regarded as an nnovative discovery, enabling the Romans to create complex structures such as the arch and the dome.
Engineers built their forts on modified terrain – often chosing the summit or the side of a low hill, near a river or stream. Roman strongholds were built by a specialist corp that included a chief engineer; much of the manual work was undertaken by soldiers. Officers known as metatores were sent to mark out the ground for an encampment, using a graduated measuring rod known as a decempeda. Each fort was erected with a wide ditch, and also included a stockade or defensive barrier made of timber posts or stone. The Romans used the residue earth from the ditch to create a rampart. While tradition dictated that each fort had four stone gateways, it was equipped with watchtowers that could reach an impressive nine metres (30 feet) high.
The fort worked on many levels – it served as a barracks, hospital, workshop, granary and stables. Every structure included a main street that ran unimpeded through the camp. In the centre was a parade yard and a commander’s headquarters. The Romans placed great emphasis on cleanliness, and so sanitary conditions were especially important. Forts had public baths and private latrines, consisting of rows of seats situated over a channel of running water. Drinking water, meanwhile, came from wells.