In the preceding pages we have determined the _role_ played by the column in Assyria, and have explained that in spite of the care and taste lavished upon some of its details, it never rose above the rank of a secondary and subordinate member. There is nothing, then, to surprise us in the fact that the Assyrian architect never placed his arches or vaults upon columns or piers; he seems never to have had a glimpse of the great possibilities such a procedure involved, a procedure from which upon the very soil of the East, his remote descendants were to evolve the architecture of the Byzantine church and the Arab mosque. His archivolts and the pendentives of his vaults always rest upon thick walls, and yet almost every variety of the simple arch or tunnel-vault are to be found among the ruins of his buildings. * * * * * [Illustration: FIG. 89.--Tomb-chamber at Mugheir; from Taylor.] Like all the other forms of Assyrian architecture the arch was invented in Chaldaea. The use of small sized materials must have led to its early discovery in that country. But the only arches now standing occur in the better preserved monuments of Assyria. On the other hand the tombs of Lower Chaldaea furnish more than one example of that false, corbelled or off-set vault, that we have already encountered in Egypt.[280] The chamber figured below is taken from the necropolis of Mugheir, formerly "Ur of the Chaldees." It is built of crude brick bound with mud. The vault is supported by walls sloping upwards and outwards like those of a modern tunnel (Fig. 89).[281]