of this nature are not infrequently connected with hieratic tradition, and if my conjecture is correct it might serve in some measure to support the claim to a non-secular character which had been put forward for Chehâr Qapû, although the domed hall, which we must assume to have been the sanctuary, bears no resemblance to the cella and anteroom of the Babylonian or of the Assyrian temple. It would be necessary to postulate that while the Sasanian builder retained in the courts and chambers of his temenos something of an ancient tradition which had come to be regarded as sacred, he gave to the shrine wherein the holy element burned with a perpetual flame the form which had been assumed by the ceremonial dwelling of the divine Chosroës. The two remaining Sasanian buildings which it will be necessary to mention are Ctesiphon and Karkh. Ctesiphon is the most famous of all the later Persian palaces (Fig. 19). It was erected by Shapûr I (A.D. 242-272)[180] and is therefore about 100 years later than Hatra, and earlier than Qaṣr-i-Shîrîn by some 250 years. Not only chronologically, but also in plan, it is closely related to the Parthian palace. It reproduces in yet more striking dimensions the simple lîwân scheme, of which Hatra offers the earliest monumental example. The lîwân at Ctesiphon is covered by a vault spanning 25·80 metres, a dimension which was not exceeded in Rome itself. On either side of the lîwân five vaulted chambers were set at right angles; rising in stories their vaults abutted the main vault, as at Firûzâbâd and Ukhaiḍir. The side chambers had an independent entrance in the façade, a system which was first employed at Hatra. The masonry is of brick, chained with wooden beams as at Ukhaiḍir; but at Ctesiphon the beams are placed parallel with the coursing of the masonry, whereas at Ukhaiḍir they are inserted at right angles into the walls. [Illustration: FIG. 19. Ctesiphon. (From _L’Acropole de Suse_, by kind permission of M. Dieulafoy.)] [Illustration: FIG. 20. Karkh. (From _L’Art antique de la Perse_, by kind permission of M. Dieulafoy.)]