Of the Anglo-Saxon cathedrals in wood or stone nothing remains. The architectural history of the present cathedral commences with the accession of the second Norman prelate, William of St. Carilef, or St. Calais on the southern border of Maine, who was bishop from 1081 to 1095, and is said to have laid the foundations of the Norman cathedral in 1093 on August 11th. The building operations of the Norman cathedral admit of a threefold division: (1) The choir and choir aisles; the arcade and triforium of the eastern aisles of both transepts; the crossing; the first bay of the nave and the first arch of the nave-triforium; and the whole of the outer walls of the nave up to the top of the aisle-arcade of intersecting arches. All this is supposed to have been built by William of St. Carilef between August 11th, 1093, and January 6th, 1096; _i.e._, in two and a half years; which seems impossible. (2) In the interval of three years between Carilef’s death and the appointment of Ralph Flambard, the monks are said to have finished the transepts. (3) Between 1099 and his death in 1128, Ralph Flambard finished the nave. These three divisions are architecturally correct; they are borne out by differences of detail; and they follow the same order of building which was observed elsewhere. But it does not follow that the exact dates given above, on mediæval authority, are correct. The most important matter is the date of the high vaults. From architectural evidence it is pretty clear that the vaulting was executed in the following order: (1) the vaults of the aisles of the choir and transepts, said to be not later than 1099; (2) the high vault of the choir, now destroyed, said to be not later than 1104; (3) the vaults of the aisles of the nave, said to be not later than 1128; (4) the high vaults of the transepts and nave, said to be not later than 1133. The chronology of the high vaults is a very important question in the history of mediæval architecture, especially as affecting the reputation of English architects. If the above dates are correct, it was the Durham architect, and not a Frenchman, who was the first to solve the great problem of mediæval architecture: how to construct and keep up a ribbed vault, oblong in plan, over a central aisle. With it goes the question of priority in the use of flying-buttresses to take the thrust of a high vault. If the dates given above are correct, Durham was a generation ahead of the whole world in the construction of a high vault and in the use of flying-buttresses. [Illustration: WEST TOWERS.] But the transverse arches of the vault of the nave are pointed; a feature which occurs nowhere else in England at so early a date. Besides, it seems impossible that if the Durham people had solved the problem of problems of mediæval architecture—the construction of a high oblong vault—nobody else should have copied it in England for more than fifty years.