The Roman walls and bastions discovered in 1889 and subsequent years under the Norman or medieval earthworks of Cardiff Castle have been described by the late Mr. John Ward, F.S.A., in Archaeologia and Archaeologia Cambrensis. It may be recalled that the remains indicate a quadrangular enclosure some 8½ acres in extent, with central gateways in the north and south sides and with semi-octagonal bastions along the walls. The fort thus corresponds closely in size and general character (though not in detail) with that at Porchester, and clearly represents a westerly branch of the coastal defence system instituted, or at least extended, in the reigns of Diocletian and Constantine I. It stands in the middle of the Monmouthshire-Glamorganshire lowlands where, alone in Wales, Roman civil life developed on a scale sufficiently extensive to require special protection from Irish or Teutonic raiders.