The largest of three guardhouses that have survived from the Edo period (1603-1867). Located between the San no Mon and Naka no Mon gates, this guardhouse controlled access to the honmaru main compound of Edo Castle. The name means “100-man Guardhouse”. The 45-metre-long building was manned day and night by four shifts of samurai, each consisting of 100 low-ranking doshin samurai and 20 higher-ranking yoriki samurai.