Kōshū Kaidō
In 1634, during the Edo period, as the outer moat of the Edo Castle was built, a number of temples and shrines moved to the Yotsuya area on the western edge of Shinjuku. In 1698, Naitō-Shinjuku had developed as a new (shin) station (shuku or juku) on the Kōshū Kaidō, one of the major highways of that era. Naitō was the family name of a "daimyō" whose mansion stood in the area; his land is now a public park, the Shinjuku Gyoen. In 1898, the Yodobashi Water Purification Plant, the city's first modern water treatment facility, was built in the area that is now between the park and the train station.