The Sasanian conquerors came out of lands on which Hellenism had made an impression less deep than on Mesopotamia, lands where Rome had never penetrated; and they came of a stock more tenacious of its own traditions and less eclectic than the Parthians. To a large extent they re-orientalized the territories which they occupied. No doubt there was less for them to copy, for in the interval of some 300 years during which the Parthians were predominant, Seleucid monuments must have disappeared, and the blurred Arsacid copy of Greek or Roman models had taken their place. The Sasanians created an art of their own, less dependent than that of Parthia on Western forms, and more potent to influence those who came into contact with it, not excluding the Byzantines. In the earliest of their palaces, so strongly marked is the reversion to Achaemenid types that Dieulafoy relegated it unhesitatingly to the earlier Persian period. In its general characteristics the plan of Firûzâbâd differs little from that of an Achaemenid khilâni palace (Plate 73, Fig. 2). The lîwân has deepened, and the employment of the vault has enabled the builder to dispense, as at Hatra, with the columns that sustained its roof. The greater depth of the lîwân, combined with a desire to keep the vaulting span within moderate bounds, have led to the breaking up of the tower room on either side into two narrow chambers. In order to counteract more effectually the thrust of the main vault (13·30 metres wide) the side chambers are placed at right angles to the lîwân, a principle which was not adopted at Hatra, but which rules at Ctesiphon, and at Ukhaiḍir. The towers themselves have disappeared, and though their place remains in the plan, in the elevation it is probable that the façade presented an unbroken line. The audience hall of the khilâni palace is reduced to a domed chamber, and the clumsy construction of the dome makes it evident that the builder would not have ventured to stretch its diameter further. Finally, round the posterior courtyard are grouped, besides the living-rooms, two smaller lîwâns, placed, like those in the Ukhaiḍir courts, so that they may serve respectively for winter and for summer. The resemblances in detail between the Achaemenid palaces and Firûzâbâd are no less striking. The high fluted gorge and narrow torus of stone which cover the doorways and niches of the one are repeated in the plaster-work of the other. The plain fillets which surround the openings at Persepolis reappear at Firûzâbâd, but in the latter case all the openings are arched, and the moulded archivolt is set within the rectangle formed by the fillets. The ṭâqchah niches, which, so far as my knowledge goes, are found for the first time in the palace of Darius, are present also at Firûzâbâd,[133] and henceforth assume a permanent place in Persian architecture, from which they were borrowed by Mohammadan builders.