Baghdad is the capital of Iraq and the second-largest city in the Arab world after Cairo and the second-largest city in West Asia after Tehran. It is located on the Tigris river. In 762 AD, Baghdad was founded as the capital of the Abbasid Caliphate, and became its most notable major development project. Within a short time, the city evolved into a significant cultural, commercial, and intellectual center of the Muslim world. This, in addition to housing several key academic institutions, including the House of Wisdom, as well as a multi-ethnic and multi-religious environment, garnered it a worldwide reputation as the "Center of Learning".