The Indus Valley civilization flourished between 2600-1900 BC along the Indus River valley in modern-day Pakistan and northwestern India. Houses in Indus cities were made of mud bricks and had thick walls to stay cool. Some houses contained a single room while larger homes had multiple rooms arranged around a central courtyard with no windows facing the street. Streets in Indus cities were narrow and alleyways branched off to more private neighborhoods. Houses commonly had indoor and outdoor kitchens and granaries, some over 150 feet long, indicated a highly developed agricultural society.