"Sumer was a civilization of clay. They made their buildings of it and wrote on it, too. Their statues were of gypsum, which dissolves in water. So the buildings and statues have since fallen apart under the elements. But the clay tablets were either baked or else buried in jars. So all the data of the Sumerians have survived. Egypt left a legacy of art and architecture; Sumer's legacy is its megabytes."