St. Mercurius Church (also known as Abu Seifien) in Cairo, dedicated to the Coptic "saint of the two swords," was built in the 6th century and underwent intensive restoration during the 12th century. It is in the heart of Coptic Cairo but off the beaten tourist track, allowing for more atmosphere and quiet than can often be had in the Hanging Church.

According to legend, Mercurius was given a sword by an angel in order to fight against the barbarians in the 3rd century. He was martyred, but he later appeared to Emperor Julian the Apostate during a battle against the Persians and pierced him with a sword. Mercurius is always represented in Coptic art as a horseman holding two swords.

The Church of St. Mercurius consists of two churches one on top of the other, with many little side chapels dedicated to various saints. The pulpit is one of the most beautiful in Cairo, decorated with mosaic and supported by 15 marble columns. A door in the north aisle of the main church leads into a courtyard with a baptistery and three sanctuaries. Fine frescoes were recently discovered in the southern gallery of the upper church, and are being restored.