Upon the Usk, the old castle of Newport has long been replaced by a later structure, but parts of Usk Castle, some miles higher up, are old, and Abergavenny, which descended from De Braose through Cantelupe and Hastings to the Nevilles, is still held by the chief of that family, though little remains of it save the original mound. It was at Abergavenny Castle that William de Braose slaughtered, in 1175, a number of unarmed Welshmen, in revenge for the murder of his uncle, Henry of Hereford. Caerleon, between Newport and Usk, though founded by a Norman upon an earlier English site connected with very celebrated Roman remains, was the heritage of a Welsh family, and continued long in their occupation. Between the Usk and the Wye the ground, in itself strong, was strongly occupied. Upon the Monnow were placed Scenfrith and Grosmont, which with Whitecastle formed the famous trilateral, so important in the war between Henry III. and the Earl of Pembroke. The keep of Scenfrith is a round tower of early date placed within a right-lined enclosure. Though small, it was very strong, and its remains are tolerably perfect. Grosmont, also of early date, is somewhat larger, and its remains are also considerable. White Castle is an enormous shell of lofty walls and mural towers placed within a most formidable ditch, beyond which are very extensive outworks both of masonry and earth. It stands very high, commands a most extensive view, and its defences are wholly artificial. All these three castles are reported to have been originally Welsh seats; but their earthworks have an English aspect. They were obviously intended for the general defence of the country, and, as usual, were always in the hands of the great Lords or of the Crown; there were besides several smaller castles or fortified houses, the centre of private estates. Of these were the castles bordering the chase of Wentwood: Dinham, long since a ruin; Penhow, the cradle of the House of Seymour; Pencoed, which still retains some early masonry; Llanvair, built by the Pain or Pagan family; and Castroggy, where is seen a part of the hall and some other masonry. Upon the Ebbw, west of Newport, stood the small castles of Greenfield and Rogeston, and at Castleton is a mound, said at one time to have been accompanied by masonry. On the hill above Ruperra is a very large and very perfect moated mound, but without any trace or tradition of masonry. Llangibby is an old Monmouthshire castle.