This area of Cairo is so-named as it contains the remains of the ancient Roman fortress of Babylon and also overlaps the original site of Fustat, the first Arab settlement in Egypt (7th century AD) and the predecessor of later Cairo. The area includes the Coptic Cairo, which holds a high concentration of old Christian churches such as the Hanging Church, the Greek Orthodox Church of St. George, and other Christian or Coptic buildings, most of which are located over the site of the ancient Roman fortress. It is also the location of the Coptic Museum, which showcases the history of Coptic art from Greco-Roman to Islamic times, and of the Ben Ezra Synagogue, the oldest and best-known synagogue in Cairo, where the important collection of Geniza documents were discovered in the 19th century. To the north of this Coptic enclave is the Amr ibn al-'As Mosque, the first mosque in Egypt and the most important religious centre of what was formerly Fustat, founded in 642 AD right after the Arab conquest but rebuilt many times since.