Anadolu Kavagi:

This fortress is often called "the Genoese Castle", but it is actually Byzantine in foundation, although the Genoese may have repaired or rebuilt it to a certain extent, when they took control of it in the mid 14C. The evidence of Byzantine origins is found in many inscriptions of Greek letters on its walls. The fortress is the largest on the Bosphorus almost twice the area of Rumeli Hisan. Most of it is occupied by the military today and off-limit to the public.