In addition to the fosse already described, the castle, and indeed the whole peninsula, was further protected by a great wall which crossed from one side to the other. According to Mr Weld’s measurements, this wall is 564 yards in length from water to water, its distance from the castle-fosse being 700 yards. “Nearly in the middle of it is an arched gateway, with its defences still tolerably entire, twenty-four feet deep, and presenting a front of twenty-one feet: between this gate and the water at either side there are square towers, at unequal intervals of from sixty to ninety yards, advanced about thirteen feet beyond the line of the walls, and being in breadth about fifteen feet: in the interior the dimensions are about eight feet six inches. These towers doubtless afforded stations for the archers, and also facilitated the access to the parapet and banquette of the wall. Whether there ever had been a fosse on the outer side, I am unable to say; the probability is, that there was; but if so, the ground has been levelled, and the rank luxuriance of vegetation has obliterated its lines. The building of the wall, however, appears in many parts to have been hastily executed, and cement to have been sparingly used, yet it still remains a most interesting monument of the military works of past ages.” Of the ecclesiastical edifices of Rinn-duin, but small remains exist, and as their names are lost to tradition, it is difficult now to identify them with certainty. The principal ruin, which is situated near the draw-bridge over the great fosse, on the land side, is most probably the church erected in the commencement of the thirteenth century, and dedicated to the Holy Trinity. Neither windows nor doorways exist to give any idea of its style, but its walls are in sufficient preservation to show the form and dimensions of the building. Like most important Irish churches it consists of a nave and choir; the nave is sixty feet long and twenty-four feet wide, the choir thirty-three feet long and eighteen wide. This church, it may be presumed, stood in a conspicuous part of the town; but not a vestige now remains of any other edifice, either ecclesiastical or domestic, between the castle and the fortified wall across the isthmus. The rude remains of the other ecclesiastical buildings are situated on the outer side of the fortified wall, and are connected with a burial-ground still much used; but there is nothing in these remains worthy of particular notice.