Judging from the bas-reliefs the corner columns of a building were generally more massive than those which were intermediate (cf. Fig. 14, C, D), a circumstance which added not only to the stability of the building itself, but also to the elegance of its appearance. But in both Babylonia and Assyria the column was used more often as an adornment to the façades of buildings than as an actual support for the structure itself. As we have so little positive evidence of the use of stone columns in Mesopotamia, it seems probable that as a rule columns were made of wood or bricks, the disappearance of almost all trace of which would be adequately accounted for by the natural destructibility of such materials, though the disappearance of stone columns, for such were clearly used, at all events sometimes, might be readily explained on the supposition that they had been subsequently used as rollers or for some other purpose. THE ARCH It has been truly said that the arch was first invented by people whose building materials were of a small size, and however open to objection this generalization may be, it is certainly true in the case of Babylonian architecture, and also in a somewhat lesser degree in that of the later Assyrian architecture. Strabo informs us that “all the houses in Babylonia were vaulted”—διὰ τήν ἀξυλιαν—“because the dearth of wood,” XVI, 1, 5—but however reliable or unreliable his statement may be, the dearth of wood and stone in the alluvial plain of Lower Mesopotamia of necessity taxed the inventive powers of the Babylonian architect to the utmost, when he was confronted with the problem of roofing the buildings he had erected, and the various rooms which they were destined to contain. But his genius seems to have arisen to the occasion, and evolved the principle of the arch as the best, and indeed the only means of coping with an otherwise insurmountable difficulty, for the construction of flat roofs depended on the existence of slabs of stones or timber-beams, alike large in size and durable, but both stone and wood of the kind wanted were not to be found in Babylonia, and the architect would clearly be unable to fetch wood or stone from the distant mountains for the purpose of roofing the chambers of an ordinary house. His inventive faculties were thus stimulated by the urgency of the case, and the result produced by these combined factors is to be seen in the early appearance of the arch, crude indeed as regards its structure, but none the less involving the same principles upon which all arches are built.