San'yōdō

San'yōdō (山陽道) refers to both an ancient administrative region and a modern road network in Japan.

As an ancient administrative region, San'yōdō was one of the Gokishichidō (Five Home Provinces and Seven Circuits) established during the Asuka period (538-710) and formally defined under the Ritsuryō system of governance. This circuit encompassed the southern portion of Honshu, the main island of Japan, facing the Seto Inland Sea. The name translates roughly to "Sunny Side of the Mountain Road," indicating its location south of the Chūgokuji Mountains.

The San'yōdō region comprised the following provinces:

• Harima Province (播磨国)
• Mimasaka Province (美作国)
• Bizen Province (備前国)
• Bitchū Province (備中国)
• Bingo Province (備後国)
• Aki Province (安芸国)
• Suō Province (周防国)
• Nagato Province (長門国)

These provinces are largely within the present-day prefectures of Hyōgo, Okayama, Hiroshima, and Yamaguchi.

In modern Japan, San'yōdō also refers to the route of the San'yō Expressway (山陽自動車道) and the San'yō Main Line (山陽本線) railway. These transportation arteries generally follow the same geographical path as the ancient San'yōdō, connecting major cities and towns along the Seto Inland Sea coast of Honshu. The term is sometimes used more generally to refer to the entire region serviced by these transportation links.