2. The true vault oversailing the wall occurs in numerous tomb chambers (_Hatra_, ii, Figs. 100, 105, 125, 130, 144, 145, 149, 152, 163), as well as in most of the smaller rooms of the inner palace (_Hatra_, ii, Figs. 225, 226, 237, and Plate 8) (Plate 74, Fig. 2). It is a form which originated in brick building. It is found in Assyrian brick tombs,[107] but never, so far as my knowledge goes, in any dressed stone vaults save in those of Hatra. It appears at Ctesiphon in the side vaults,[108] and in the rough stonework of Qaṣr-i-Shîrîn (Plate 52, Fig. 2, and Plate 68, Fig. 1). It is constant at Ukhaiḍir and in early Mohammadan architecture,[109] and it is used invariably in the brick vaulted constructions of Mesopotamia at the present day. It is perhaps the triumphant survival of the old brick vault of horizontal oversailing courses, represented by Mughair, and it bears, at Hatra and elsewhere, another indubitable mark of its brick origin in the horizontal or almost horizontal joints of its lower courses.[110] 3. The vault springing flush with the walls is used in tombs (_Hatra_, ii, Figs. 103, 118, 128, 139, 159), in the southern and in the northern lîwâns of the main palace and in the two lîwâns which were added at the northern end (_Hatra_, ii, Plate 8), in the western annex, the so-called temple (_Hatra_, ii, Plate 9), and in building B (_Hatra_, ii, Fig. 183). The moulded cornice, which usually divides this vault from the walls below, is absent in most of the tombs. The high stilt formed by the horizontal lower courses, which is especially remarkable in the larger of these vaults, differentiates them from western Hellenistic vaulting and connects them more closely with brick forms. In one of the smaller palaces there is a striking example of the survival of brick building methods (_Hatra_, ii, Fig. 74). The stone vault is composed, almost to its whole height, of horizontal courses, and only the very top of the arch is filled in with radiating voussoirs. Nor is the elliptical vault, which is the form naturally assumed by oriental uncentered brickwork[111] wanting at Hatra (_Hatra_, ii, Figs. 108 and 162, Fig. 162 being a primitive example, where the vault is carried down to the floor of the chamber).