I want to go to Wales again, where would you recommend for Roman ruins?

I was in Wales a few years ago, and only for a few days, so I don't think I can be much help. I visited more castles than Roman ruins (some of those I saw in England). I went to Caernarfon castle, along with Flint, Denbigh and Rhuddlan castles. I don't recall seeing any specific Roman ruins in those areas. I do know that some English road atlases have castles and ruins marked right on the map--that's how I visited the places I did--I just followed the map. I don't know if you can get those altases in the States, though.