This is the city's largest church (UNESCO World Heritage) and the main sanctuary dedicated to its patron saint, Agios Dimitrios; it stands on the presumed site of his martyrdom c 306. Restored after the fire in 1917, in line with the original architectural plans, the church has retained some features that are of incomparable historical and artistic interest: the 7C Byzantine mosaics decorating the pillars on either side of the entrance to the apse are remarkably delicate and refined.