On AgiouDemetriou str. one can see a church that is dominating and unique among many other Orthodox temples of the same period, the Church of Agios Demetrius, dedicated to the city's patron saint, Saint Demetrius. The church is a Hellenistic type five-aisled basilica characterized by the impressive painting and marble decorations and by ornate capitals dating from the 5th century. In the basement of the church is the place where the Saint was martyred, while among the mosaics unique is the one that depicts the Saint with two small children between the bishop and the eparch who restored the temple in the 7th century A.D. 

The primary temple (A.D. 313) was only a small spot for prayer, a prayer-book there where Saint Demetrius was tortured and martyred. The prayer-book was destroyed and in its place was built in A.D. 629 to 634 a five-aisled basilica, the Saint Demetrius church. Since A.D. 904 the temple was looted by various conquerors – Saracens, Normans – and even the relics of the Saint which were kept in a special box (kivorio) were removed. In 1978, the skull and parts of the relics of the Saint were returned and placed in a silver reliquary, made by the Filippotis house in Τinos. 

With the fall of the Byzantine Empire, the temple was converted into a mosque with the name KasimieMosque and became once again an Orthodox Christian church in 1912. The church was completely destroyed in the great fire of Thessaloniki in 1917 and was reconsecrated after the restorations, on October 26, 1946, the date that the Saint is celebrated by the church. 

Since 1988, the Church has been designated by the UNESCO as a Cultural Heritage Monument.