Old Segontium occupies the summit of a hill, about a quarter of a mile to the South East of the present Town, and is intersected by the road leading to Bethgelert; its ancient British name was Caer Sallawg: {91} it is about 150 yards in length, and 100 wide; some remains of the Roman Walls are still visible, (now covered with Ivy) particularly near the South East corner. Some years back there appeared the remnant of a building, made with tiles, and plaistered with very hard and smooth mortar; this is supposed to have been part of a _Hypocaust_. The mortar in all other parts is very hard, and mixed with much gravel, and sand. This ancient Station forms an oblong of very considerable extent, seemingly from four to six Acres. Camden suspects that this might have been the _Setantiorum_, Porlus of Ptolemy being willing to read it _Segontiorum_, but the situation of the former is certainly at the mouth of the Ribble. He is most probably right, in supposing it to have been, in after times, named Caer Cwstenin, or the Castle of Constantine; and that _Hugh Lupus_, who certainly invaded Anglesey, in 1098, had here a temporary post. Mathew of Westminster asserts, (but upon what authority is not mentioned) that Constantius, father of Constantine, was interred here, and that Edward caused the body to be taken up, and honourably reburied in the Church, (probably of St. Publicius). Mr. Rowlands in his history of Anglesey says, that Helen, the supposed mother of this reputed Saint had a Chapel {92} here, which, he tells us, was in being in his days. Near the steep Bank of the Seiont, about one hundred yards from the end of Pool Street, and divided by the road leading to Clynnog and Pwllheli, are the ruins of a Roman Fort, connected, no doubt, with Old Segontium, and intended, as it is conjectured, to protect the landing from the river.—On two sides the walls are pretty entire, one is seventy-four yards long, the other sixty-four; height ten feet eight inches, thickness six feet. A great part of the facing is taken away, which discovers the peculiarity of the Roman masonry; it consists of regular courses, the others have the stones disposed in zigzag fashion. Along the walls are three parallel lines of round holes, not three inches in diameter (nicely plaistered within) which pass through the whole thickness. There are other similar holes, which are discovered in the end of the Wall, and some to run through it lengthways. There are various conjectures respecting the use for which these were intended, the most probable is, that they were for the purpose of holding the scaffolding, which were supported, it is likely, by cylindrical iron bars, and when taken out, the air was admitted to harden the mortar, which was poured into the work in a liquid state. Near one corner, some years ago, the foundation of a round Tower was discovered; it was paved, and in it were found the horn of a deer, and skeletons of some lesser animals.