The Bible and Sumerian and Babylonian myths recorded a catastrophic flood sent by the gods to destroy humankind. With the assistance of the gods, one man (variously called Noah, Ziusudra, or Utnapishtim) and his family survived by building a boat. The discovery of the legend by George Smith in 1872 in Ashurbanipal's library at Nineveh, in cuneiform tablets telling the epic of Gilgamesh, was very close in details to the Old Testament story of Noah. It is assumed by many that the stories derive from a common source. At Ur in 1929, Leonard Woolley revealed a depth of 2.5 m of silt separating the Ubaid and Uruk levels, a deposit he could account for only by just such a flood. It should be noted, however, that flood levels have been found at other sites whose dates can be more appropriately equated with Noah's. Today many archaeologists believe that the various flood stories do not represent the record of a single event, but rather a whole series of natural disasters which affected the low-lying alluvial plain of southern Mesopotamia.