The Romans founded the town in AD 75 as a market town - venta in their Latin - for the defeated Silures, the Brythonic tribe of south-east Wales. The Silures had fought Rome harder than most. The historian Tacitus, writing of their campaigns against the legions, describes them as fierce and resourceful, holding out for years in the difficult country between the Severn and the Wye. When they were finally subdued, Rome did not destroy them. Roman policy in the provinces was to absorb. The Silures were given a tribal capital, organised on the standard Romano-British civitas model, and named Venta Silurum to distinguish it from other tribal markets such as Venta Belgarum (Winchester) and Venta Icenorum (Caistor St Edmund). The name 'Caerwent' itself preserves the original: caer is the later Welsh word for a fortified place; -went is what remained of Venta. The Welsh kingdom of Gwent that came after the Romans took its name from the same Latin root.

Large sections of the Roman town walls remain in place. The historian John Newman called them 'easily the most impressive town defence to survive from Roman Britain, and in its freedom from later rebuilding one of the most perfectly preserved in Northern Europe.' What makes Caerwent extraordinary is precisely the absence of later building: most Roman towns in Britain were swallowed by medieval cities that reused the stone and rebuilt the lines. Caerwent never grew into a medieval city. The walls were left alone. Excavations in 1971 dated the polygonal angle-tower at the north-west corner to the mid-fourth century. In 1881, a gardener digging behind a cottage uncovered a piece of intricate Roman floor mosaic - tessellated stone showing different kinds of fish, the kind of decoration that might have floored a wealthy townhouse's dining room. Channel 4's Time Team filmed Wessex Archaeology working through the site in 2008.

Most of the houses excavated at Caerwent were unsophisticated. Few had mosaic floors. Few had the underfloor heating system called hypocaust. The town was large, but it was not luxurious. Archaeologists read this as evidence that Caerwent was a working market for ordinary provincial Britons - a place where local Silures came to trade, pay taxes, attend the basilica, hear judgements, take part in the slow Romanisation of their tribal culture. It was not Bath; it was not St Albans; it was not one of the showpieces of Roman Britain. It was something more interesting: a working tribal capital where Britons and Romans rubbed along together for three centuries. Modern houses now occupy half the site of the old Roman marketplace, but the ruins of several Roman buildings remain visible, including the foundations of a fourth-century temple with its temenos - the sacred enclosure that surrounded the building.

When Roman administration collapsed in Britain in the early fifth century, Caerwent did not. The town remained an important centre through the early medieval period - the place where the road from Gloucester to Caerleon crossed the north-south road from Shrewsbury, via Monmouth and Trellech, down to the sea at Portskewett. Excavations have uncovered post-Roman metalwork - elaborate penannular brooches and clothing pins - dated to the fifth, sixth, and seventh centuries. A large number of Christian burials, some in stone-lined graves, have been found from between the fourth and ninth centuries, both around the eastern gate and close to the parish church. One tradition holds that Caerwent may even have been the birthplace of Saint Patrick - though the claim, like many Patrician traditions, has more enthusiasts than evidence. A monastery was established here before the tenth century, and a pre-Norman cross head was discovered on the site in 1992.

Modern Caerwent has lived an oddly military second life. During the Second World War, a Royal Navy Propellant Factory was established immediately to the north of the village, on the other side of the A48. Between 1967 and 1993, the site was used as a storage station for the Royal Air Force and the United States Army. Since then it has served as an army training facility - and, by way of variety, as a filming location: the Doctor Who episode 'Before the Flood' was shot here, and so was material for Captain America: The First Avenger. The village itself, bypassed by the A48 and quietly shrinking, has lost most of its pubs - the Northgate Inn closed in 2013, leaving the Coach and Horses as the only one - but the Post Office is still busy and the village garage has been repairing cars on the same site since 1917. The Romans laid out the streets nearly two thousand years ago. People are still walking them.