One of the most distinctive features of Harappan cities was the carefully planned drainage system. At the Lower Town, the roads and streets were laid out along an approximate grid pattern, intersecting at right angles. It seems that streets with drains were laid out first and then houses were built along them. If domestic waste water had to flow into the street drains, every house needed to have at least one wall along the street. It is certainly the most complete ancient system as yet discovered. 134. Prove with the help of examples that the Harappans had established their contacts with Western Asia for purchase/exchange of artefacts.