wheel: the most distinctive vessel of the Uruk period, the beveled rim bowls, were hand-moulded. Metallurgy Metallurgy also seems to have developed further in this period, but very few objects survive. The preceding Ubayd period marked the beginning of what is known as the chalcolithic or 'copper age', with the beginning of production of copper objects. The metal objects found in the sites of the 4th millennium BC are thus above all made with copper, and some alloys appear towards the end of the period, the most common being that of copper and arsenic (arsenical bronze), the copper-lead alloy being also found, while the tin bronze does not begin to spread until the following millennium (although the Late Uruk Period is supposed to be the beginning of the 'Bronze Age'). The development of metallurgy also implies the development of long-distance trade in metals. Mesopotamia needed to import metal from Iran or Anatolia, which motivated the long-distance trade which we see developing in the 4th millennium BC and explains why Mesopotamian metalworkers preferred techniques which were very economical in their use of raw metal. Architecture In architecture, the developments of the Uruk period were also considerable. This is demonstrated by the structures created in the Eanna district of Uruk during the Late Uruk period, which show an explosion of architectural innovations in the course of a series of constructions which were unprecedented in their scale and methods. The builders perfected the use of molded mud-brick as a building material and the use of more solid terracotta bricks became widespread. They also began to waterproof the bricks with bitumen and to use gypsum as mortar. Clay was not the sole building material: some structures were built in stone, notably the limestone quarried about 50 km west of Uruk (where gypsum and sandstone were also found). New types of decoration came into use, like the use of painted pottery cones to make mosaics, which are characteristic of the Eanna in Uruk, semi-engaged columns, and fastening studs. Two standardised forms of molded mud-brick appear in these buildings from Uruk: little square bricks which were easy to handle (known as Riemchen) and the large bricks used to make terraces (Patzen). These were used in large public buildings, especially in Uruk. The creation of smaller bricks enabled the creation of decorative niches and projections which were to be a characteristic feature of Mesopotamian architecture thereafter. The