The greater part of Lower Egypt, the Nile delta north of ancient Memphis, which is in marked contrast with Upper Egypt's valley. Though it has equally important history, its remains are now lost, buried beneath many meters of the silt which has accumulated since ancient times. The lowercased term refers to any flat alluvial tract built up by the deposition of silt at the mouth of a river. The name derives from the fact that the Nile fans out into several tributaries as it approaches the Mediterranean, creating a triangular area of fertile land shaped like the Greek letter delta.