There was a corresponding row of moulded column bases in the inner court of the Principia at Housesteads, where they were interpreted as indicating the line of a colonnade which had been supported against the wall separating the inner from the outer court.

Its Five Rooms

Entering off the inner court was a row of five rooms just as we find at Birrens, at Chesters, and at Gellygaer. Hardly anything remained but the whinstone cobble foundations of the dividing walls. In Plate X., Fig. 2, we have a portion of the main outer wall of the second chamber from the north side of the building (6). It exhibits the formation of the cobble substratum. The different character of part of the masonry is probably due to some subsequent alteration of the building. The foundations of the walls on either side of the central room were four and a half feet wide, the others only four feet. A few stones of the scarcement course of the north wall of the central chamber remained in position, from which it seemed probable that the wall itself had originally been three and a half feet thick. The wall resting on the four feet foundation may have been about three feet. This distinction in thickness of the walls has been noted elsewhere, and is no doubt due to the fact that the central chamber formed the Sacellum, and contained the shrine of the standards, while beneath its floor was preserved the military treasure, often placed in an underground vault. Over the ruined floors of the four outer chambers lay a stratum of fine gravel, and in the debris were many fragments of large red flanged tiles which had fallen from the roof above.

The Strong Room

Within the central room were the foundations of a small inner chamber which appeared to have been set into it (5), and which measured about eleven feet square. It did not appear to belong to the original plan of the building, for the walls, which were about a foot thick, had been built of old materials, and did not run parallel to those of the room in which they had been placed. Moreover, in digging a foundation for the east wall of the interior chamber the cobble foundations of the wall of the larger room were exposed, showing that the smaller chamber had been sunk lower than the flooring of the original room. This is clearly shown in Plate X., Fig. 3, in which the foundations are viewed from the west. In the centre of the north wall were the remains of a stair. The courses on one side of the entrance remained to a height of twenty inches, and showed the rebate for the door, which must have opened inwards. The lower step of the stair which remained was about three feet long. The masonry was rough. The