The Castle was sited above the River Usk overlooking the river valley and the confluence of the River Gavenny with the River Usk on a site that would have been naturally defensible in earlier times, and may well have been a fortified site from Bronze Age and Iron Age periods was then also favoured by the Romans, who built their Roman fort of Gobannium on the same hilltop just a little to the west of the site later developed into the Castle. With steep slopes down to the river on three sides, the remaining side was where the town under the protection of the Castle developed, over what must have been the Roman fort and settlement site. The main Castle gatehouse faced the town, which was later walled.
