Baghdad (/ˈbæɡdæd, bəɡˈdæd/; Arabic: بَغْدَاد [baɣˈdaːd]) is the capital of Iraq and the second-largest city in the Arab world after Cairo. It is located on the Tigris near the ruins of the ancient Akkadian city of Babylon and the Sassanid Persian capital of Ctesiphon. In 762 CE, Baghdad was chosen 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 multiethnic and multi-religious environment, garnered it a worldwide reputation as the “Center of Learning”.