The edifice was erected by Sir William St. Clair, third Earl of Orkney, who succeeded to the estates about 1417. About thirty years afterwards he founded the Collegiate Church of Rosslyn. Certain letters which occur on shields along the cornice of the north wall have been ingeniously deciphered by Dr. Thomas Dickson, of the Register House, Edinburgh, as the initial letters of the following words,[83] viz.:--WILZAME · LORDE · SINCLARE · FUNDIT · YIS · COLLEGE · YE · ZEIR · OF · GOD · MJJJJL. The structure appears, however, to have been begun a few years earlier, about 1446, as in the year 1447 the continuator of the _Scotichronicon_ says, “Dominus Willelmus de Sancto Claro Comes Orcadiæ _est in fabricando sumptuosam structuram apud Roslyn_;”[84] and probably the foregoing inscription refers to some ceremonial event connected with the building. Sir William died in 1484, and he appears to have left the building very much in the condition in which we now find it. In that case its erection would be the labour of about forty years. The church was a collegiate foundation, for a provost, six prebendaries, and two singing boys or choristers, and was dedicated to St. Matthew. It consists (Fig. 1070) of a choir with north and south aisles, connected [Illustration: FIG. 1071.--The Collegiate Church of Rosslyn. View from South-East.] by an aisle which runs across the east end, and gives access to a series of four chapels beyond it to the east. The dimensions of the building are as follow, viz.:--interior--length of choir, 48 feet 4 inches; width of central aisle, 17 feet 10½ inches; width over aisles, 35 feet; total exterior length, 69 feet 8 inches; height to the apex of the roof, 41 feet 9 inches. The original intention was to have completed the building as a cross church, with choir, nave, and transepts, but the choir only has been completed. The transepts have been partly erected, the east wall being carried up to a considerable height, but the nave has not been erected. The length across the transepts, as founded, is about 72 feet. Mr Thomson, the custodier of the chapel, who saw the west walls of the transept exposed, states that the transepts were intended to be 18 feet wide, as drawn on Plan. The Rev. Mr. Thompson, Rosslyn, in his guide to the chapel, says that the foundations for the entire building had been laid, and that those of the nave, which extended to about 91 feet to the west, were dug up and exposed at the beginning of the present century. This exactly corresponds with the length which the nature of the ground would permit.