The Indus valley civilization started in 3000 BC. This civilization started because of the Indus river, the Arabian sea and the mountains surrounding the valley. It is said to be the largest empire till the Persian empire happened which was not till 900 years later. The hard-working and religious people of this civilization grew cotton for a living( only the people at the bottom of the social class pyramid).That was their main trading commodity.

A picture of a little drain in Mohenjodaro!

This people had excellent organization skills. The proof lies in the cities carefully planned in perfect blocks, their excellent underwater channels taking the water to each house and all the drains taking the dirty water away from the house. Also each road was perpendicular to the other one giving it a perfectly planed look. I'm throwing in a little fact there: This people invented the concept of bathrooms and had one in each house!