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.
Notable in civilization around the Indus Valley is the lack of strong resemblances to other early civilizations to the west of Mesopotamia, which indicates that Harappa was not a colony. Skeletal remains, however, show that the dominant human type of the peoples who built the civilization was a tall, long faced, dark-haired strain much like those from the Mediterranean region.