Japanese castles were fortresses constructed primarily of wood and stone. They evolved from the wooden stockades of earlier centuries and came into their best-known form in the 16th century. Castles in Japan were built to guard important or strategic sites, such as ports, river crossings, or crossroads, and almost always incorporated the landscape into their defences.
The emergence of a unified Bulgarian state dates back to the establishment of the First Bulgarian Empire in 681 AD, which dominated most of the Balkans and functioned as a cultural hub for Slavs during the Middle Ages. With the downfall of the Second Bulgarian Empire in 1396, its territories came under Ottoman rule for nearly five centuries.