The lower zone of the north façade forms part of the decorative scheme of the central court as a whole. The central court resembles, as has been observed by Dr. Reuther, a Greek peristyle with engaged columns in place of free standing columns; the southern side is, however, treated as a separate façade, the façade of the lîwân. The principal feature was necessarily the wide arched opening of the lîwân itself. There is nothing new here; we have it at Ctesiphon, combined with Hellenistic wings; we have it at Firûzâbâd, without side doors, and at Sarvistân and at Hatra. Hatra, though in plan it is no less purely oriental than Ctesiphon, shows direct Western influence far more strongly than the southern Mesopotamian or the Persian palaces. Dr. Herzfeld has compared its triple-arched façade, wherein the central arch surpasses the flanking arches in height and width, with that of the triumphal arch,[352] and the comparison is apt. So far as my knowledge goes, the triple-arched scheme appears for the first time in the Assyro-Persian cultural sphere at Hatra, and it is accompanied there by strongly Hellenized details of decoration, which distinguish it from the older oriental palaces to which it is related in plan. This Hellenized decoration is present in all other Parthian ruins, and it is not surprising that it should be so. The Parthians wrested their empire from a Greek dynasty. The Mesopotamia which they conquered was a part of Asiatic Greece; it was more closely linked to Greek culture than it had ever been linked before, or was ever to be linked again. The Hellenistic triple-arched scheme fitted the lîwân plan admirably, inasmuch as it provided the great opening which was essential to the lîwân hall. But it implied the placing of doors in the two flanking chambers, and this was done for the first time at Hatra. The side doors were an innovation which was not accepted without hesitation. It was not adopted in the façade of Firûzâbâd, where Hellenistic influence is almost entirely lacking. To a great extent the Sasanians stand for a reaction against Hellenism. A fresh wave of orientalism flows back into Mesopotamia with their conquest, and they went far to complete the severance with the West which the Parthians had begun when they overthrew the Seleucids. But the Greek domination, together with the fitful occupation of parts of northern Mesopotamia by Roman armies, left an indelible mark. Moreover, the Sasanian frontiers marched with those of Rome, and the interpenetration of the two civilizations was inevitable. It is felt in the façade of Ctesiphon. Though the triple-arched scheme is not present there, the provision of independent doors to the side chambers was a convenience; it was used at Firûzâbâd in the lîwân group at the back of the posterior façade; it was used at Ctesiphon, and thereafter it was not to disappear. With it the triple-arched façade came into favour. It formed part of the truly oriental façade of Sarvistân; no doubt it