The Basilica of Saints Nereus and Achilles was built in the 4th century in the Celio district, not far from the Baths of Caracalla. In 814 Pope Leo III rebuilt the Church near the old titulus to house the relics of the two martyrs moved from the Catacombs of Domitilla. Over the centuries, the Church underwent a long period of decadence, until 1475, when Sixtus IV began a first restoration, then completed in 1600, when the furnishings of the presbytery and the frescoes that decorate the interior were made. In the 19th century the ancient mosaic of the apsidal arch, dating back to the 9th century, was restored. The facade, "a salienti", is decorated with geometric frescoes by Girolamo Massei. Coeval to the frescoes is the marble prothyrum, supported by two Corinthian columns and consisting of a triangular tympanum. On either side of the apse you can recognize the ancient turrets (795-816), later transformed into a rectory and sacristy. The interior, richly frescoed with cycles of saints' lives, has the typical basilica plan: a nave and two side aisles, divided by octagonal pillars. The high altar, built with three panels, contains the relics of Saints Nereus, Achilles and Domitilla. Behind the altar there is the episcopal throne in cosmatesque style (Vassalletto's school; the apse arch is decorated with mosaics from the 9th century.
