Historic Wales is an excellent map based interface that has several layers, including the National Monuments Record for Wales, Listed Buildings, HERs, Scheduled Ancient Monuments and the National Museum Archaeology Collection. You can also overlay the mapping on the 1st edition OS map. Very basic site details in each site’s infobox link to a much fuller record on Coflein. From a Roman roads perspective, it is a shame that all sites are presented as points, not lines or polygons.
The online catalogue of archaeology, buildings, industrial and maritime heritage in Wales. You can search records of sites, as well as the online catalogue of photographs, drawings, manuscripts and digital resources and view over 125,000 images. Coflein has the option of using it’s own mapping interface, and whilst it might at first to duplicate parts of Historic Wales, the two sites are quite different in many ways. The information for each site also links to any available images.
Archwilio is the easy way to discover the archaeology of Wales through the records of the four Welsh Archaeological Trusts. There is some dublication with the Historic Wales site - Archwilio will only give the records from the Welsh HERs.