above these horizontal courses the tiles are laid upright and in slices; they form an ovoid curve more abrupt than the curve of the lower part of the vault. The fourth of the upper chambers, reckoning from east to west, is the best preserved. It shows the remains of a doorway, 1·85 m. wide, covered on the same principle as the small doors of the mosques, _i.e._ without lintel or arch. A moat or trench runs all round the castle and passes to the north of the gatehouse. A bridge, of which small trace remains, connected the gatehouse with a rectangular outpost. To the north and east of this outpost there are fragments of a wall and towers which encompassed a rectangular area.[135] The most interesting feature in the ruins is the niche decoration between the bastions of the north wall (Fig. 148). The niches have been in part filled up--no doubt they were found to be too dangerous a weakness to the wall--but their scheme is clearly apparent (Fig. 144). Each niche consisted of a high cusped arch above a rectangular recessed panel which enclosed in turn a smaller arched niche. High up on the wall, near the western angle tower, there are traces of an upper order of niches. There is some indication that the niches were continued in the first north bay of the west wall, but the remainder of this wall, together with the whole of the east wall, is completely ruined. The disadvantage of these deep niches is evident in the south wall where the niche has been broken through at its weakest point and has now the appearance of a door. In the two central towers on this side there seemed to have been small flat-roofed chambers (Fig. 147). The building materials used in the castle are burnt and sun-dried brick. The foundations of the [Illustration: FIG. 146.--SÂMARRÂ, EL ’ASHIḲ FROM NORTH.] [Illustration: FIG. 147.--SÂMARRÂ, EL ’ASHIḲ FROM SOUTH.] [Illustration: FIG. 150.--SÂMARRÂ, ṢLEBÎYEH.] [Illustration: FIG. 151.--SÂMARRÂ, ṢLEBÎYEH, SETTING OF DOME.] walls and towers, the vaulted substructures, the niched face of the north wall and its towers, together with what remains of the south wall and towers are of burnt brick, but all the rest of the structure, including the partition walls of the gatehouse, are of sun-dried brick, and the same material is used to fill up the niches in the north wall. [Illustration: FIG. 149.--ṢLEBÎYEH.]