There is one keep which is known to be of the reign of Stephen, though not built by him, that of Carlisle, built by David, King of Scotland, in 1136,[1162] a time when he thought his hold on the four northern counties of England was secure, little reckoning on the true character of his great-nephew, Henry, son of Matilda. There is no advance to be seen in this keep on those of Henry I., except that the walls are faced with ashlar. The vaulting of the basement is pronounced by Mr Clark to be very evidently a late insertion.[1163] With the reign of Henry II. a new era opens as regards the documentary history of our ancient castles, because the _Pipe Rolls_ of that king's reign have most fortunately been preserved.[1164] These contain the sheriff's accounts for money spent on the building or repair of the king's castles, and are simply invaluable for the history of castle architecture. The following is a list of the keeps which the _Pipe Rolls_ show to have been built or finished by Henry II.:-- Scarborough, built between 1157 and 1174. Tower Windsor, " " 1161 " 1177. Shell wall Orford, " " 1165 " 1172. Tower Bridgenorth, " " 1166 " 1173. Tower Newcastle, " " 1167 " 1177. Tower Bowes, " " 1171 " 1187. Tower Richmond, " " 1171 " 1174. Tower Chilham, " " 1171 " 1173. Tower Peak, " " 1172 " 1176. Tower Canterbury, " " 1172 " 1174. Tower Arundel, " " 1176 " 1182. Shell wall Tickhill, " " 1178 " 1181. Tower The dates given here must be taken as only roughly accurate, as owing to the meagreness of the entries in the _Pipe Rolls_, it is not always certain whether the expenses were for the great tower or for other buildings. The list by no means includes all the work which Henry II. did on his English castles, for he was a great builder; but a good deal of his work seems to have been the substitution of stone walls with mural towers, for wooden stockades, and our list comprises all the cases in which it is clear that the keep was the work of this king.[1165] We confine our attention to the keeps, because though mural towers of stone began to be added to the walls of baileys during Henry II.'s reign (a detail which must have greatly altered the general appearance of castles), it is certain that the keep was still the most important part, and the residence of the king or noble whenever he visited the castle.