Venta Silurum is the ruined Roman town at Caerwent, once the tribal capital of the Silures. The best reason to come is the scale of what remains: stretches of town wall still rise several metres, with traces of houses, the forum-basilica, and a Romano-British temple inside.
It is an easy historical side trip from Chepstow if you want Roman Wales without a museum case between you and the stones. The site is quiet, open, and much easier to read if you take time to follow the walls.