The architecture of a country is determined very largely by the materials with which nature has endowed that country; it is also influenced by the configuration of the country itself as well as by the climate whose effects it is the builder’s object to either regulate or counteract. The physical characteristics of the Mesopotamian Valley as also the climatic conditions which prevail there have already been under consideration, but it will not perhaps be unfitting to devote a few pages to a review of the materials which were used for building operations, before we proceed to discuss the ruins of the buildings themselves. It has been already stated, that practically no stone at all is to be found in the low-lying and marshy country of Babylonia, hence it never assumed an important place in Babylonian architecture; any stone required, had to be quarried far away in the mountains and transported at great labour, in consequence of which it was only employed for exceptional purposes and in cases where the desire for permanent durability rendered it necessary. Accordingly the stone used was generally diorite, basalt, or some other hard stone of volcanic origin, contrasting strikingly with the softer stone utilized so freely by the Assyrians. Assyria on the other hand was more fortunate in this respect and afforded a very fair supply of limestone and alabaster which were used extensively by her sculptors and builders, though the clay so easily procurable all over the valley was the one indispensable element in the erection of temples, palaces, or houses in both countries. The supply of wood again was extremely scanty not only in Babylonia but also in Assyria, and any wood used for columns, lintels or thresholds was generally brought from Lebanon, Amanus, or some other distant place. We thus see that the art of brick-building was almost forced upon the dwellers of Mesopotamia from the very necessity of the case. The clay used for the purpose was by no means uniform either as regards its colour, or as regards its quality. Sometimes it is of a light yellow colour, sometimes it is almost black, while the clay from which other bricks are made is of a reddish hue. Those made of light yellow clay are the best from the point of view of durability. The bricks further vary both in size and shape according to the period to which they belong, so that it is often possible to provisionally assign a date to a building or the remains of a building by an examination of the style of brick employed. The type of brick characteristic of the early periods of Sumerian history is that known as the plano-convex[48] type; thus the kiln-burnt bricks of which the storehouse of Ur-Ninâ, the first king of Lagash, was composed, are oblong and plano-convex, while each of them also bears the impression of a thumb-mark on the convex side.