Located in Western Macedonia, the city of Kastoria is the capital of the prefecture of the same name. It lies between the Verno (Vitsis) and Grammos Mountains, on a narrow peninsula which widens as it projects into Lake Orestiada, also known as Lake Kastoria. Its geographical location and naturally fortified position, described by Anna Comnena when her father Alexius I Comnenus besieged the city, rendered it one of the major hubs in Western Macedonia. This was a decisive factor in the city’s economic and cultural development.

The first evidence of habitation in the area’s long history can be traced back to the Neolithic era. According to written sources, in the pre-Christian era the site of present day Kastoria was occupied by Keletron or Kilitron, one of the cities of Orestida along with Diocletianoupolis and Argos Orestikon.

Procopius the historian relates that in the 6^th century Justinian founded a new fortified city on the site, naming it Diocletianoupolis after a ruined city of the same name nearby. Written sources from the 10^th century onwards refer to it as Kastoria.

As part of the fortification projects undertaken by Justinian to organize the defences of imperial cities, the neck of Kastoria Peninsula was closed off by a wall reinforced with semi-circular and round towers. Controlled access to the city was gained via three gates; the central one lay only 100 metres from the bridge over the moat outside the city walls.

The only Early Byzantine monuments still surviving in the city are some sections of the wall, reused architectural members (spolia ) in the Church of the Archangel of the Metropolis, and a capital found on the west side of the Koursoumli Mosque, which lends weight to the hypothesis that there was a Christian basilica in the area.

In addition to the isthmus wall, from Early Byzantine times there was an interior wall around the citadel. This began on the northwest side, ran parallel to both shores of the lake and ended in the area to the north and east of the Church of Panagia Koumbelidiki, incorporating it into the city. The enclosure wall had at least six gates linking the citadel to the city.  When the Byzantine fortifications were reconstructed, a massive tower was built to further strengthen the main gate in the Justinian wall at the neck of the city.

The link to the Via Egnatia facilitated communication between Kastoria and the centre of the empire at Constantinople. Proof of relations with the capital throughout the Middle Byzantine period is mainly to be seen in the cultural influences apparent in monuments.

Both within and beyond the walls, the number of churches surviving from the 9^th to the late 14^th century attests to a flowering of the city at that time. The churches in question are small three-nave basilicas , such as Agios Stephanos and Agioi Anargyroi; single-nave churches, such as Panagia Mavriotissa and Agios Athanasios; and triconch churches, such as Panagia Koumbelidiki. The most striking feature of the three-aisled basilicas in Kastoria is a prominent central nave with raised sides, punctuated by single and double light windows . The surviving iconographic programmes are impressive, as is the ornate ceramoplastic decoration on the exterior, featuring courses of clay tiles in the shape of rectangles, squares, parallelograms and triangles. These often run like friezes around the top of the walls under the roof, or surround the body of the monument at various heights. Several of these churches were private, and many served as the catholica of small monasteries in Kastoria. It is worth noting that most of the sites were in continuous use, as is evident from the fact that the churches were rebuilt and decorated more than once.

The city has a turbulent history. From 927 to 969 it was occupied by the Bulgarians, who were expelled by the Pechenegs with encouragement from the Byzantines. In 990 Tsar Samuel of the Bulgarians raided Greece and conquered Kastoria. It was liberated in 1018 by Basil II and became his military operations base. In 1082 the city was taken by Bohemund , son of the Norman leader Robert Guiscard. It was recaptured by Alexius I Comnenus a year later, at the beginning of what proved to be a lasting peace, which resulted in a new peak of prosperity.

The city may have been occupied by the Normans for a few months at the end of the 12^th century, when they crossed Western Macedonia en route from Durres to Thessaloniki in the summer of 1185. Kastoria seems to have been an important commercial centre with a strong Venetian presence, as indicated by a chrysobull issued in their favour by Alexius III Angelus in November 1198.