of construction the architect seems to have bethought him that such protection was necessary and to have added a strong girdle to his palace plan. On the other hand, the Sasanian palaces, so far as they are known to us, are either unfortified, or they stand within a fortified park, the walls and towers of which are not in direct structural relation with the residential buildings. At the same time Sasanian military works, where they have been examined, do not differ materially from those of Ukhaiḍir; the fortress of Qala’-i-Khusrau at Qaṣr-i-Shîrîn is an excellent case in point (Plate 73, Fig. 1). It is a rectangular enclosure, about the size of Ukhaiḍir (roughly 180 metres square), surrounded by a wall which is strengthened by rounded towers. The towers are somewhat differently disposed from those of Ukhaiḍir; they are larger and they are set twice as far apart, but the scheme is the same in both places. The interior buildings are much ruined. A row of chambers, or more probably, from the width of the ruin heaps, a row of small courts with chambers grouped round them, adjoined the inner side of the walls, leaving a central court which was partly filled by a large building, rectangular in plan. The town wall of Dastadjird was also furnished with rounded towers.[77] Almost without exception the plan of the Sasanian palaces is a development of the lîwân type, the origin of which is to be sought in the southern Hittite sphere, northern Syria and the mountain lands north of the Mesopotamian plain. The architecture of this region is known to us best through the excavations at Zindjirli, where the evolution of the southern Hittite palace can be traced over a period of close upon a thousand years.[78] It is an evolution which is dominated [Illustration: FIG. 5. Zindjirli. (From _Ausgrabungen in Sendschirli_, by kind permission of the D. Orient-Gesellschaft.)] from the first to last by the monumental gateway. At Zindjirli the type appears in its earliest and simplest form in the gateways of the inner city wall, which Professor Koldewey places approximately in the thirteenth century before our era.[79] A doorway set back between a pair of solid towers leads into a narrow [Illustration: FIG. 6. Pasargadae. (From _Iranische Felsreliefs_, by kind permission of the authors.)]