Its eastern end is a semicircular vault, while on the western side a narthex, flanked by towers, and traces of an exonarthex survive.

At the eastern end of the northern side aisle, a middle Byzantine chapel dedicated to St. Irene is attached.

[5] The surviving parts of the church's rich original interior decoration include particularly fine 5th-century Ionian capitals from a Constantinopolitan workshop, the green Thessalian marble columns of the tribelon, the original Proconnesian marble pavement of the central nave, and fragments of 5th-century decorative mosaics.

Fine but damaged early 13th-century frescoes depicting the Forty Martyrs of Sebaste adorn the southern side.

Underneath the north aisle's current pavement, three layers of floor mosaics from an earlier Roman-era bath have been uncovered.