Babylon Fortress

Babylon Fortress is an Ancient Roman fortress on the eastern bank of the Nile Delta, located in the area known today as Old Cairo or Coptic Cairo. The fortress was built circa 300 AD by Emperor Diocletian in order to protect the entrance to an ancient canal, previously rebuilt by Trajan, that linked the Nile with the Red Sea.

It was at the boundary between Lower and Middle Egypt, where the river craft paid tolls when ascending or descending the Nile. Within the fortress's former enclosure are the present-day Coptic Museum, a convent, and several churches, including the Church of St. George and the Hanging Church.

Source: Wikipedia