Their commemorative gateways are of interest, as they have a central opening and a smaller one on each side, like the Roman triumphal arches; the heads are square, however, with brackets in the corners. The upper parts are ornamented with figures in relief and inscriptions recording the virtues of persons to whose memory they are dedicated. Although communication existed between China and the countries bordering upon the Mediterranean from remote ages, Chinese architecture, like the Indian, was without influence upon that of Europe. It is only in Western Asia that the first forms of building are discernible, which were subsequently imitated or followed in European constructions. The most important of these are situated in Mesopotamia, the fertile region comprised between the Tigris and the Euphrates. The political histories of Assyria, Babylon, and Persia are generally treated separately, but the architecture of each belongs to one style, which may be called the Assyrian, for its distinguishing characteristics remain the same in all the great cities which were in turn the capitals of reconstructed kingdoms and empires. It may be considered in four chronological divisions: In ancient Babylon, from 2234 B.C. to 1520 B.C., at Wurka and Mugheyr; in Nineveh, from the fourteenth to the seventh century B.C., at Nimrod, Khorsabad, and Koyoundjik; in the second Babylon, during the seventh century and after the capture of the latter by Cyrus in the year 538 B.C., in Persia, at Persepolis, Passargadæ, and Susa. A renaissance of the art may be traced in Sassanian buildings erected eight centuries later. The citadels, palaces, and other important structures of these cities were usually built upon artificial mounds or terraces, strengthened by massive walls. The materials used were bituminous bricks, cemented with bitumen, slabs of gypsum anchored with copper nails and bands, and timber for roofs and columns. Stone and gypsum or alabaster were employed in Nineveh and in the cities of Persia. In Babylon the only available material was bituminous clay, and consequently all the buildings there were built of brick. At the present day nothing remains of these but irregular mounds, from which but little can be gathered toward an understanding of what their appearance was when entire. Wood was probably used to a great extent, and was naturally most easily destroyed by the fire of invading armies. The roofs, formed of thick layers of earth carried on beams, in falling in, buried the lower portions of buildings, and it is probably due to this fact that the bass-reliefs have been preserved. The surfaces of the bricks were frequently enamelled in colours, and the wood-work was probably brilliantly painted, as traces of pigments have been found upon the more durable materials.