From the royal letters of the period of the First Dynasty we know that the canals were not only used for irrigation, but also as water-ways for transport.---The letters contain directions for the bringing of corn, dates, sesame-seed, and wood to Babylon, and we also know that wool and oil were carried in bulk by water. For transport of heavy goods on the Tigris and Euphrates it is possible that rafts, floated on inflated skins, were used from an early period, though the earliest evidence we have of their employment is furnished by the bas-reliefs from Nineveh. Such rafts have survived to the present day,[23] and they are specially adapted for the transport of heavy materials, for they are carried down by the current, and are kept in the main stream by means of huge sweeps or oars. Being formed only of logs of wood and skins, they are not costly, for wood was plentiful in the upper course of the rivers. At the end of the journey, after the goods were landed, they were broken up, the logs being sold at a profit, and the skins, after being deflated, were packed on donkeys to return up stream by caravan.[24] [Illustration: FIG. 42. THE ASSYRIAN PROTOTYPE OF THE GUFA. (From a bas-relief in the British Museum.)] The use of such _keleks_ can only have been general when through-river communication was general, but, since we know that Hammurabi included Assyria within his dominions, it is not impossible that they may date from at least as early a period as the First Dynasty. For purely local traffic in small bulk the _gufa,_ or light coracle, may have been used in Babylonia at this time, for its representation on the Assyrian monuments corresponds exactly with its structure at the present time as used; on the lower Tigris and Euphrates. The _gufa_ is formed of wicker-work coated with bitumen, but some of those represented on the sculptures from Nineveh appear to have been covered with skins as in the description of Herodotus.[25]