The seat of the Coptic Orthodox Church of Alexandria, on a site traditionally identified as that of St Mark's original 1st-century foundation. The present cathedral is a 1950s structure built on much older remains; the underground crypt contains the relics of St Mark and an 11th-century cemetery of Coptic patriarchs.
Visitors are welcome outside service times. The cathedral is part of the larger Coptic Patriarchate complex, which also includes a small museum of liturgical objects and manuscripts. Dress modestly; the staff are generally friendly to respectful visitors. The Greek Orthodox Cathedral of the Annunciation is nearby, providing context for Alexandria's parallel Christian traditions.