Nagurumi Castle was built in 1578 by Sanada Masayuki, a retainer of the Takeda clan, as the base for attacking Numata Castle. In 1589, Toyotomi Hideyoshi yielded up Numata region to the Hojo clan but he allowed the Sanada clan to hold this castle as before. Inomata Kuninori, the castellan of Numata Castle got angry at this decision and attacked Nagurumi Castle in November in the same year, with which Hideyoshi expressed his dissatisfaction and attacked the Hojo clan to their extinction. This is what is called “the Incident of Nagurumi Castle,” which lit the spark of Hideyoshi’s Seige of Odawara and allowed him to take the opportunity to unite the country. San-no-kuruwa (the third compound), Sasa-kuruwa, Sode-kuruwa, and the watch tower remain to the present time. Each of the compounds is divided by the moat and the building layout of the foretime is well preserved. Hannya-kuruwa and Mizunote-kuruwa (the compound for water intake) called “Maruyama” also remain to the present time.