The Roman town
Venta was founded by the Romans in AD 75 as a market town for the defeated Silures tribe in Roman Wales. In fact, Venta Silurum seems to mean "Market town of the Silures"  (cf. Venta Belgarum and Venta Icenorum). This is confirmed by inscriptions on the "Civitas Silurum" stone, now on display in the parish church.
The town, located on the Roman road between Isca (Caerleon) and Glevum (Gloucester) and close to the Severn estuary, was - in contrast with nearby Isca - essentially established for civilian administration rather than for military purposes. The forum and basilica, the market place and centre of local government for the civitas, were built in the time of the Roman Emperor Hadrian, in the early part of the 2nd century. Public baths, Thermae, and shops, including a blacksmiths, were built about the same time. Remains of farms and dwellings, some with courtyards, have also been excavated. There was also a Roman temple, perhaps dedicated to Mars and the Celtic god Ocelus. A bowl with a chi-rho symbol gives evidence of early Christian worship from the late 3rd century.
In 2008, a dig involving Wessex Archaeology and volunteers from the local Chepstow Archaeology Society, found a row of narrow shop buildings and a villa with painted walls, frescoes of Roman art and mosaic floors. Among the artefacts excavated were a bone penknife hilt depicting two gladiators fighting, coins, Roman glassware, ceramics, human and animal bones, lead patches used for repairing and pieces of mosaic. These excavations featured in Channel 4's Time Team programme, broadcast on 25th January 2009.
The town lacked substantial defences until the mid 4th century, when stone town walls were built. A small garrison may have been based in the town during that period. Large sections of the defensive walls are still in place, rising up to 5 metres in height in places. The walls have been described as "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." In 1881 a portion of a highly intricate coloured floor mosaic or Tessellated pavement, depicting different types of fish, was unearthed during excavations in the garden of a cottage. Excavations in 1971 dated the north-west polygonal angle-tower to the mid-300s.
Modern houses are built on top of half the site of the old Roman market place. The ruins of several Roman buildings are still visible, including the foundations of a 4th century temple. The fact that most of the houses lacked mosaic or hypocaust-heated floors, however, suggests that despite its size, Caerwent never achieved the cultural level of other Romano-British tribal capitals.
After the Romans
Unusually, the site remained occupied after the Roman troops left, until at least the mid-5th century. It appears that Christian worship was already established in the town, and it may have had a bishop.. A monastery was founded by Saint Tatheus in the 6th century, and a Christian cemetery was also established around the site of the present church.
The name Venta gave its name to the emerging Kingdom of Gwent, and the town itself became known as Caer-went or "the fort of Venta/Gwent". Tradition holds that Caradog Freichfras of Gwent moved his court from Caerwent to Portskewett around the 6th century.