The ruins of the huge city of Moenjodaro – built entirely of unbaked brick in the 3rd millennium B.C. – lie in the Indus valley. The acropolis, set on high embankments, the ramparts, and the lower town, which is laid out according to strict rules, provide evidence of an early system of town planning.
Indus culture seems to have gradually spread from west to east, with sites towards central and southern India flourishing after Harappa and Mohenjo Daro had declined. The drying up of the ancient Saraswati or Ghaggar-Hakra River, east of and parallel to the Indus, may also have affected the civilization. There are numerous Indus sites along that river bed.