The Monastery of Saint John the Baptist was founded by the senator Stoudios and built between 454 and 463. In the ninth century it became the most important monastery of the capital and had great influence in all the orthodox world. The church, a basilica with three naves, galleries and a timber roof, was restored several times. In the Ottoman time, it remained in use as a mosque, but was rebuilt after a fire in 1784 and finally given up after a second fire in 1920. It is the only large surviving building that was erected before Justinian I, and still impressive as a ruin.