Hōki Province in the context of "Mimasaka Province"

San'indō (山陰道; Japanese pronunciation: [saɰ̃.iꜜn.doː]) is a Japanese geographical term. It means both an ancient division of the country and the main road running through it. San'in translates to "the shaded side of a mountain", while dō, depending on the context, can mean either a road, or a circuit, in the sense of delineating a region. This name derives from the idea that the northern side of the central mountain chain running through Honshū was the "shaded" side, while the southern side was the "sunny" (山陽 San'yō) side. The pre-modern region corresponds for the most part with the modern conception of the San'in region.

The region was established as one of the Gokishichidō (Five provinces and seven roads) during the Asuka period (538–710), and consisted of the following eight ancient provinces: Tanba, Tango, Tajima, Inaba, Hōki, Izumo, Iwami and Oki. However, this system gradually disappeared in the centuries leading up to the Muromachi period (1333–1467).

Bitchū Province (備中国, Bitchū no Kuni; Japanese pronunciation: [biꜜt.tɕɯː (no kɯ.ɲi), bit.tɕɯꜜː (no kɯ.ɲi)]) was a province of Japan on the Inland Sea side of western Honshū, in what is today western Okayama Prefecture. It was sometimes called Bishū (備州), with Bizen and Bingo Provinces; those three provinces were settled in the late 7th Century, dividing former Kibi Province. Bitchu bordered Hōki, Mimasaka, Bizen, and Bingo Provinces.

The ancient capital and temples were built around Sōja. For much of the Muromachi Period, the province was dominated by the Hosokawa clan, who resided in Shikoku and allowed the province a degree of independence. By the Sengoku Period, other clans fought over Bitchu, and Oda Nobunaga and Mōri Terumoto were fighting in the province when Oda died, leading to a division of the province. After 1600, the province was divided among a variety of han (fiefs), and included a number of castles. By the time the provinces were reorganized into prefectures, the dominant city was the port, Kurashiki.