During the Edo period, there was a plain that spanned two villages, Shimo-Shibuya and Shimo-Toyosawa, and the farmland on this plain was home to a number of Daimyō villas and retainers' mansions. This plain was supposedly renamed Hiro-o during a land survey in 1699. The plain also served as a falconry ground. Shibuyagawa River, which ran through Hiro-o Hara, was named after the various places it passed through before reaching the sea. So, depending on the place, it was named Furukawa, Shinborigawa, Akabanegawa, and Kanasugigawa.