Baghdad is the capital of Iraq and the second largest city in the Arab world after Cairo. Located along the Tigris, near the ruins of the ancient Akkadian city of Babylon and the ancient Sassanid Persian capital of Ctesiphon, Baghdad was founded in the 8th century and became the capital of the Abbasid Caliphate and the Caliphate’s most notable major development project. Within a short time, 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 multi-religious environment, garnered the city a worldwide reputation as the "Center of Learning".
Baghdad was the largest city in the world for much of the Abbasid era during the Islamic Golden Age, peaking at a population of more than a million. The city was largely destroyed at the hands of the Mongol Empire in 1258, resulting in a decline that would linger through many centuries due to frequent plagues and multiple successive empires.