he origins of the city's name, Kastoria, have long been the subject of scholarly controversy. The view that it comes from a Bulgarian noun kostur cannot be right: the name Kastoria is recorded from the reign of Justinian, long before the shortlived Bulgarian occupation of the city in the 10th century.
Others argue that the name may well come from the noun kastron (castle), a term that will
have referred to the fortifying of the city. This is also what Kastoria was known as during
Ottoman rule, while its inhabitants were often called kastriotes (castellans).
Again, the association of the city's name with its fortress by the 12th century
was clearly intended by Anna Komneni
when she wrote (Alexiad II.41):
The prevailing view nowadays, however, is that the city owed its name to the beaver (Castor fiber), the animal that once upon a time used to live on the shores of its lake.