Kuruwa (曲輪, くるわ) is a Japanese term for the walls of a Japanese castle, and the regions bounded by the arrangement of those walls. The term may also be written as 郭, and the term maru (丸) is also used for castles built after the Edo period. The kuruwa serves as a defensive territory, provides space for additional castle facilities, and contains the living quarters for common soldiers, making it an important fixture of all Japanese castles. Most castles built during the middle ages contain many kuruwa of small area, while those built during or after the early modern period often contain a lesser number of kuruwa of larger area. The western equivalent is the motte-and-bailey.
The shape and structure of a castle were important factors in determining the victor of castle sieges, and the castle layout, or nawabari (縄張) was arranged with the intention of giving the defender an insurmountable advantage. The kuruwa regions were planned for after the basic layout of the castle grounds was decided. The three basic kuruwa regions are the honmaru (本丸); the core of the castle, and the ninomaru (二の丸, lit. "second circle") and sannomaru (三の丸, lit. "third circle"), which serve as auxiliary areas.
There are three major styles of kuruwa arrangement:
Many castles use a combination of the above three styles, and may fit into multiple categories of arrangement. Some castles may not be categorizable at all. Smaller kuruwa regions called obikuruwa (帯曲輪) and koshikuruwa (腰曲輪) were sometimes placed around the central kuruwa in some arrangements. demaru (出丸) refers to a kuruwa that is placed independent from the central kuruwa, and umadashi (馬出) refers to a kuruwa that is placed specifically to guard an important entrance. See below for more related terms.
Most of the terms take the form -kuruwa or -maru, but specific terms may differ depending on region or time period. Castles that use the naming -maru were built during the early modern period. Many castles contain kuruwa named after particular people or places.