Also dorui 土塁. An earthen embankment, earthwork, or rampart. A defensive embankment surrounding a castle or a mansion is generally made of earth excavated from the moat. Accordingly, the earthen embankment and the moat are fundamentally a single entity. The doi is often joined with, or forms an integral component of, other attendant defensive installations such as palisades, *saku 柵, surrounding enclosures, *kuruwa 郭, stone-faced walls, *ishigaki 石垣, parapets and walls, *hei 塀, and entrances, *koguchi 虎口. Excavated evidence for the earliest defensive embankments goes back to the Yayoi period residences and settlements, *kangō shūraku 環濠集落. The earliest usage of the term doi for a defensive installation appears in medieval sources such as the Chikujōki 築城記, which dates back to 1565. Construction methods range from simply piling up the dirt excavated from the moat, to a more solidified construction with stonework faces. Some doi were built up using rectangular wooden frames that were filled in with dirt, wetted down, and then pounded hard, a technique known as hanchiku 版築 (block construction). A vertical section of an embankment resembles a truncated capital letter "A": wider at the bottom, gradually getting narrower as it goes upward. The outside diagonal slope, kane 矩, of the embankment is called sotonori 外法, and the inside diagonal slope is called uchinori 内法. The base is called *doijiki 土居敷, and the flat top of the embankment is called mabumi 馬踏, hirami ひらみ, or narashi ならし. The two main types of embankment are: the pounded earth embankment, *tatakidoi 敲土居, which has a relatively gentle slope; and a grass embankment, *shibadoi 芝土居, with a steeper slope. The pitch of the sides is called *kōbai 勾配. Various terms are used to describe the shape of the incline on an embankment or wall: see *ōgi-no-kōbai 扇の勾配 and *terakōbai 寺勾配. See also variations such as *hachimaki doi 鉢巻土居 and *koshimaki doi 腰巻土居. There are also distinctive defensive installations called *chōjō 長城 (long fortification).