Baghdad is the capital of Iraq and the second-largest city in the Arab world after Cairo. Located along the Tigris River, the city was founded in the 8th century and became the capital of the Abbasid Caliphate. Within a short time of its inception, Baghdad 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 hosting a multiethnic and multireligious environment, garnered the city a worldwide reputation as the "Centre of Learning".