Page:A History of Art in Chaldæa & Assyria Vol 1.djvu/252

 2^0 A HISTORY OF ART ix CIIALH.KA AND ASSYRIA. Thus we find that only at each alternate vertical course was the arch of burnt and moulded brick complete. The openings left at the summits of the other courses must have been filled in in some way, and, in fact, the line of voids which ran along the top of the extrados was filled in with brick earth, beaten tight and forming the best of keys. So that the vault was completed and consolidated by the same material as that used to make its channel impervious to water. 1 This vault has another strange singularity which at first is very surprising. The whole structure has a sensible inclination in the direction of its length, suggesting that some accident had happened to it in course of erection. Such an explana- tion must be rejected, however, because at the moment of discovery the whole arrangement was uninjured, and, moreover, the filling of clay must have rendered any movement of the kind impossible. M. Place's explanation seems the best. He thinks the slope was given merely to facilitate the work of the bricklayers. The first course of voussoirs would be sloped in this fashion, and would rest upon some mass of crude brick in the centre of the building. The bricks of the second course would o lean against it, and their weight would be brought in to add cohesion and solidity to the whole structure instead of being entirely occupied in adding to the perpendicular thrust, while the ease with which they could be placed without an internal support would be much increased. Assisted by this simple expedient, two bricklayers with their labourers could build the vault at a very rapid rate. We may believe that the notion of building in this way would never have occurred to the Assyrian architects but for their habit of dispensing with timber centres. This slope had an effect upon the arrangement of the bricks which should be noticed. In all other vaults, such as those of the city gates, the units are laid upon their longest sides, and a vertical section shows their shortest diameters. Here, on the other hand, the bricks stand on their edges, and their largest surfaces are in contact, on each side, with the next vertical course, 1 The same process was employed at Nimroud in a drain or water channel, of which LAYARD gives a sketch (Discoveries, p. 164). In connection with these vaults we must remember that a pointed arch has no key properly speaking ; the top stone is merely a joint. It looks as if the Assyrian architect had a kind of instinctive appreciation of the fact.