Japanese castle architecture, Dokuritsushiki style

The walls and the yagura towers surrounding the Japanese castles were, of course, built for defense, but they were also designed to create an interior space for the main keep (tenshukaku). Considering how the yagura were connected with the tenshu, there are several styles of construction: directly (the Fukugoshiki style) or via a more or less complex passage (the Renketsushiki style).

But the simplest version is the Dokuritsushiki style, where the main keep isn't connected to any yagura, as you can see in this wide angle photo of Maruoka-jō, the castle with the oldest tenshukaku from Japan.