An artificial valley was dug between the Kanda Plateau that stretched from Hongo to Surugadai (The areas between present-day Suido-bashi and Mansei-bashi bridges [Akihabara]) to dug to create an artificial valley so that the Hira-kawa River run through the valley, joined Naka-gawa River in the west (which originated in the Kanda Plain and poured into Sumida-gawa River) and run under Asakusa-bashi Bridge to pour into Sumida-gawa River.
今の水道橋から万世橋（秋葉原）の間は本郷から駿河台まで伸びる神田台地があったためこれを掘り割って人口の谷を造って通し、そこから西は元から神田台地から隅田川に流れていた中川の流路を転用し、浅草橋を通って隅田川に流れるようにした。