or 24th century BC), contained an immense treasure of luxury items made of precious metals and semi-precious stones imported from long distances (Ancient Iran, Afghanistan, India, Asia Minor, the Levant and the Persian Gulf). This wealth, unparalleled up to then, is a testimony of Ur's economic importance during the Early Bronze Age. Archaeological study of the region has contributed greatly to our understanding of the landscape and long-distance interactions during these ancient times. Ur was a major port on the Persian Gulf, which extended much farther inland than today, and the city controlled much of the trade into Mesopotamia. Imports to Ur came from many parts of the world: precious metals such as gold and silver, and semi-precious stones, namely lapis lazuli and carnelian. It is thought that Ur had a stratified social system including slaves (captured foreigners), farmers, artisans, doctors, scribes, and priests. High-ranking priests apparently enjoyed great luxury and splendid mansions. Tens of thousands of cuneiform texts have been recovered from temples, the palace, and individual houses, recording contracts, inventories, and court documents, evidence of the city's complex economic and legal systems. Excavation in the old city of Ur in 1929 revealed the Lyres of Ur, instruments similar to the modern harp but in the shape of a bull and with eleven strings. History Prehistory When Ur was founded, the Persian Gulf's water level was two-and-a-half metres higher than today. Ur is therefore thought to have had marshy surroundings; irrigation would have been unnecessary, and the city's evident canal system was likely used for transportation. Fish, birds, tubers, and reeds might have supported Ur economically without the need for an agricultural revolution sometimes hypothesized as a prerequisite to urbanization. Archaeologists have discovered the evidence of an early occupation at Ur during the Ubaid period (c. 6500 to 3800 BC). These early levels were sealed off with a sterile deposit of soil that was interpreted by excavators of the 1920s as evidence for the Great Flood of the Book of Genesis and Epic of Gilgamesh. It is now understood that the South Mesopotamian plain was exposed to regular floods from the Euphrates and the Tigris rivers, with heavy erosion from water and wind, which may have given rise to the Mesopotamian and derivative Biblical Great Flood stories. Sumerian occupation of the 4th millennium BC The further occupation of Ur becomes clear only during its emergence in the third millennium