The Patriarchal Cathedral feature a triple apse , the central part of which match the apse of the original basilica on the site . The three @-@ naved church follow the traditional Byzantine cross @-@ in @-@ square design . Built out of crushed stones and mortar with limited brickwork , it measure 26 by 12 metres ( 85 ft × 39 ft ) . The cathedral include two narthices , a bell tower and two other premises attached to the south church wall . The presence of a bell tower is considered to be a rarity in Balkan church architecture . Six columns support the interior and distinguish the altar from the cella ( naos ) . It is unclear whether the church housed a synthronon ( stone benches for the clergy ) in the apse , as there are doubts that its remains may actually be part of the older basilica .