Saint Mercurius is the largest in the district of
ancient Babylon. It is located at the north of the Fortress of Babylon in
Old Cairo .The Church of Saint Mercurius is perhaps the only one in
Cairo with its original foundation intact. It stands 31.5 meters long by 21 meters wide. However, the church itself was demolished and turned into a sugarcane warehouse, but was rebuilt under Patriarch Abraham (974-979). Afterwards, in 1080, 47 bishops met in the church by order of the Fatimid vizier Badr Al-Gamal to establish the
Coptic canons. Many Coptic patriarchs resided in the church during the 11th through the 15th centuries, and later during the 16 and 18th centuries, others were consecrated in the Church of St. Mercurius. The church also came to be the final resting place for many church leaders. The entrance to this church leads to the narthex, separated from the nave by a fine wooden screen. There are huge piers that divide the nave from the north and south aisles. The eastern piers help support the large cupola; build during restoration after a fire late in the 12th century, which surmounts the khurus, a transverse room preceding the sanctuary, and the sanctuary. The nave itself has an arched, wooden roof.
