MORTAR
The layers and courses of clay bricks of which the buildings in Mesopotamia were for the most part composed, were cemented together by mud in the earliest times; this clay-mud is generally distinguishable from the bricks which it unites by the difference of its colour. Mud-mortar has been found on some of the earliest sites and in some of the most ancient buildings, while in Assyria it appears to have been the regular form of cement used at all times. In the city of Babylon, strange to say, clay mortar appears to have been used instead of lime or asphalt in the late buildings of Sassanidian times. This mud-mortar consisted of clay mixed with water and perhaps a little straw, as was the case in the cone-wall at Warka,[51] while sometimes reeds embedded in clay were laid between the bricks, as was the case at both Warka and Hammam, but at an extremely remote period the Babylonian architect began to avail himself of the rich supply of bitumen gratuitously yielded by the soil of his native land, for the purpose in question.
The most famous bituminous springs in Mesopotamia were those at Ḥit on the Euphrates. Their fame had reached Egypt as early as the time of the eighteenth dynasty, for Thothmes III brought bitumen thence to Egypt. Herodotus a millennium later—about 450 B.C.—alludes to Ḥit as famous for her bitumen, and subsequent writers make similar mention of the springs there. A good example of the early use of bitumen in Babylonia was found at Abû Shahrein, the site of ancient Eridu, where a very early building was excavated by Taylor, the antiquity of which was proved by the pre-Sargonic plano-convex bricks used in its construction, and these bricks were all laid in bitumen; the same was found to be the case in a building composed of finger-marked bricks at Ur (Muḳeyyer), all of which were embedded in bitumen.
The platform upon which Ur-Ninâ’s storehouse at Tellô was erected consisted of three layers of plano-convex and finger-marked bricks, all set in bitumen, while in the building underneath that of Ur-Ninâ, bitumen was also freely used.[52]
In like manner at Nippur, the finger-marked bricks of which the city-gate was constructed were laid in bitumen, though the bricks composing the early arch found on this site were set in mud, probably an indication that at the time when the arch was built bitumen was not used; around the base of Ur-Engur’s ziggurat on the other hand there was a coating of bitumen, while the crude brick altar found by Haynes in the lowest stratum at Nippur had a rim of bitumen; but in later times it was supplemented by the more tenacious lime-mortar, though only partially was this the case, for even as late as Nebuchadnezzar’s time (604-561 B.C.) its practical utility as a preventive against the destructive forces of rain were still recognized, the burnt brick retaining walls of his palace at Babylon being actually laid in bitumen. In like manner the bricks composing the old fortification wall, are rendered adhesive by means of a lavish prodigality of asphalt, so adhesive in fact, that it is often very difficult to separate them. Fortunately the side bearing the stamped inscription has its face downwards and therefore is not in immediate contact with the asphalt from which it is separated by the layer of reeds and clay already alluded to.
In the later buildings at Babylon, however, lime-mortar is also used, the transition period being marked by the employment of both in one and the same building, and in point of fact Koldewey found that in the case of one of the walls of a building of Nebuchadnezzar, one half of the wall was cemented together by means of asphalt, while in the other half lime-mortar alone was used. But in the new castle which Nebuchadnezzar built for himself on the Kasr, the very finest materials were employed, the bricks being of a pale yellow colour and extremely hard, contrasting with the bricks used in his earlier buildings, which are of a reddish-brown colour and less durable, while in this new structure, pure white lime-mortar alone is used. Lime-mortar, as well as mud-cement and bitumen, was employed at Nippur, as also at Birs-Nimrûd (Borsippa), and the mortar used has such adhesive properties that the bricks can only be separated by breaking them, while at Muḳeyyer (Ur) a mortar composed of a mixture of lime and ashes was employed.
In Assyria on the other hand, mortar seems to have been used more sparingly; when stone was employed as a building material, generally speaking no cement of any kind was used, the stones being carefully dressed so as to permit of no interstices, as for example was found to be the case with the stone retaining-wall round the ziggurat at Nimrûd; when ordinary crude bricks were employed, they were laid in a sufficient state of moisture to render them adhesive; while when burnt brick was the material in question, the mortar adopted was a mixture of clay and water. Bitumen however was by no means unknown in Assyria, but it was used chiefly under pavements or the limestone floors of sewers, to prevent leakage or infiltration.