The position of the motte of Old Sarum is exceptional, as it stands in the centre of the outer fortress. This must be owing to the position of the ancient vallum, encircling the summit of one of those round, gradually sloping hills so common in the chalk ranges, which made it necessary to place the motte in the centre, because it was the highest part of the ground. The present excavations have shown that it is in part artificial. But though the citadel was thus exceptionally placed, the principle that communication with the outside must be maintained was carried out; the motte had its own bailey, reaching to the outer vallum. The remains of three cross banks still exist, two of which must have enclosed the _magnum ballium_ which is spoken of in the _Pipe Rolls_ of Henry II. Probably this bailey occupied the south-eastern third of the circle, which included the main gateway and the road to the citadel. In the ditch on the north side of this enclosure, an arched passage, apparently of Norman construction, was found in 1795; it was doubtless a postern or sallyport.[642] The main entrance is defended by a separate mount with its own ditch, which is conjectured to be of later date than the vallum itself. The area of the top of the motte is about 1-3/4 acres, a larger size than usual, but not larger than that of several other important castles.[643] In Leland's time there was "much notable ruinous building" still remaining of this fortress, and the excavations have already revealed the lower portions of some splendid walls and gateways, and the basement of a late Norman keep which presents some unusual features.[644] The earthworks, however, bear witness to a former wooden stockade both to the citadel and the outer enclosure. The top of the motte is still surrounded by high earthen banks. As that great building bishop, Roger of Salisbury (1099-1139), is said to have environed the castle with a new wall,[645] it would seem likely that he was the first to transform the castle from wood to stone. But in Henry II.'s reign, we find an entry in the _Pipe Rolls_ for materials for enclosing the great bailey. An order for the destruction of the castle had been issued by Stephen,[646] but it is doubtful whether it was carried out. The sums spent by Henry II. on the castle do not amount to more than £266, 12s. 5d., but the work recently excavated which appears to be of his date is very extensive indeed. The mention of a small wooden tower in Richard I.'s reign shows that some parts of the defences were still of wood at that date.[647] Timber and rods for _hoarding_ the castle, that is, for the wooden machicolations placed at the tops of towers and walls, were ordered at the end of John's reign.[648]