One of my favorite Byzantine monuments in Thessaloniki is the church of the Holy Apostles. What makes it unique is the combination of gorgeous frescoes and mosaics; even though the latter, only fragments are preserved! The dedication to the 12 disciples of Christ is a modern invention because, according to some popular beliefs, the building should have had 12 domes! That is impossible, and there are only five domes.
The monument was a monastery church located near a gate of the western walls of Thessaloniki. It was founded by the Patriarch of Constantinople, Niphon I, around 1310-1314, as testified on the lintel of the entrance of the west and some monograms (schematic renderings of his name). The second founder, abbot Paul, who was Niphon’s disciple, is depicted kneeling before the enthroned Mother of God in the inner narthex (vestibule). At around 1520-1530, the church was turned into a mosque. The Ottomans’ modifications caused serious damage to the interior decoration because they covered the sacred figures and scenes with plaster. However, that doesn’t undermine the importance and beauty of the monument. Make sure you also have a look at the exterior masonry with the various decorative patterns. You won’t regret it!