Fig. 17.—Cross-section of a lion relief (B) and of an Assyrian relief (A).
With the help of these models, moulds could be made for each separate brick. They were probably of burnt pottery similar to the moulds made for the abundant terra-cottas of Babylonia. The mould would form one side of the frame in which the brick was struck, and, according to the regular method of bonding, a course of whole bricks (33 × 33 centimetres) would be followed by a course of half bricks (33 × 16½). Thus the ground of the reliefs and the wall surface were actually identical, and there is not even a projecting base on which the paws of the great beasts might appear to rest, as would be the case with stone reliefs. This is art in clay, a specialised art, distinguished from all other kinds of relief. The edges of the figures do not project more or less squarely as they do in Assyrian alabaster reliefs (Fig. [17] A), but in an obtuse angle (Fig. [17] B). Also there are no even upper surfaces as there are on Assyrian stone carvings. Both peculiarities would considerably facilitate the withdrawal of the tile from the mould.
The same conception of art influenced the marvellous, highly developed, glyptic art of Babylonia. The style of the gem reliefs during the time of Hammurabi was also transferred to stone, while the older Babylonian stone reliefs distinctly show their direct derivation from the previous flat bas-reliefs, to which Assyrian art of the later period still adhered. Previous to our excavations no example of the plastic art of the time of Nebuchadnezzar was known.
The brick when moulded and before it was enamelled was burnt like any ordinary brick; the contours were then drawn on it with black lines of a readily fusible vitreous composition, leaving clearly marked fields. These were filled with liquid coloured enamels, the whole dried and then fused, this time apparently in a gentler fire. As the black lines had the same fusing-point as the coloured portions they often mixed with the colours themselves, thus giving the work that marvellous and harmonious brilliancy and life which we admire to-day. With the Persian enamels which we shall meet with in connection with the Persian buildings these black lines have a higher melting-point and therefore remain distinct and project above the coloured enamels after the firing.
The bricks had then to be arranged according to the design. In order to facilitate this and to ensure an accurate distribution of them on the building site, the bricks were marked on the upper side in rough glaze with a series of simple signs and numerals. The sign on the side of a brick and on that which was to be placed next it are identical. We shall learn more of the system in the Southern Citadel, where it was employed in the enamelled decorations of the great court.
A complete study of these details could not be made in Babylon as we were cramped for space and could not spread out the pieces. The chemical preservation of them was carried out in Berlin with great care under the able direction of Professor Rathgen. The antiquities from the ruined sites, more especially the pottery, were completely permeated with salts, saltpetre, and the like. These materials, owing to long exposure to air, had formed hard crystals on the surface, which had to be removed by long-continued soaking. Here in Babylon also we numbered each piece so that we could be certain at what part of the Processional Street each fragment had been found. The transverse cut in the wall u 13 of the plan of Kasr (Fig. 13) gives an excellent insight into the method of construction. Over every course of brick is a thin layer of asphalt, and above this an equally thin layer of mud and then another course of bricks. The joints of the course, which are from 1 to 1½ centimetres thick, are also formed of asphalt and mud. In every fifth course a matting made of reeds, the stalks of which have been split and rendered flexible by beating, is substituted for the mud. The matting itself has rotted, but the impression left on the asphalt is still perfectly fresh and recognisable. In appearance it corresponds exactly with the ordinary matting in use in the neighbourhood to-day.
A determined and very remarkable effort was obviously made to separate the courses, to prevent their adhering to each other, overlaid as they were with asphalt. This separation occurs in other parts of the city effected by reed straw instead of mud. Only in some few detached instances were the bricks laid immediately on the bitumen, where they fitted together as firmly as a rock, as in the wall 17 metres thick which in k 13 runs through the great Principal Citadel, in the southern strongest part of the Ishtar Gateway, and also in the postament of the cella in the temple of Borsippa. We may add that asphalt and mud, or asphalt and reed straw are regularly used for joints throughout the period of the Babylonian kings. Only in his latest buildings, the Kasr, the Principal Citadel, and Babil, did Nebuchadnezzar change to lime mortar, while Nabonidus for his Euphrates wall turned once more to asphalt. The later builders, Persians, Greeks, and Parthians, employed mud for mortar.
The asphalt mortar in the great defensive walls of Babylon and the inserted mats are mentioned by Herodotus (i. 179): he records that after every 30 courses of bricks a plaited mat was inserted. So large a number has not yet been observed by us. The lowest number is 5, the highest 13. In the Babylonian, inscriptions on buildings, especially on those of Nebuchadnezzar, asphalt is very often mentioned in connection with burnt brick, but never mud, lime, or reeds.
VI
THE ISHTAR GATE
The magnificent approach by way of the Procession Street corresponds entirely with the importance, the size, and the splendour of the Ishtar Gate. With its walls which still stand 12 metres high, covered with brick reliefs, it is the largest and most striking ruin of Babylon and—with the exception of the tower of Borsippa which, though now shapeless, is higher—of all Mesopotamia (see ground-plan on Fig. [46]).