Shiroi Castle




The actual date of construction for this castle is unknown but it was most likely built around 1429-1441 by Nagao Kagenaka. Kagenaka was allied with Uesugi Kenshin, but after his death there were disputes by the Uesugi, Hojo and Takeda to take these lands. In Hideyoshi's siege of Odawara (1590) the Nagao were allied with the Hojo. When confronted with the combined forces of Maeda Toshiie and Uesugi Kagekatsu the Nagao easily surrendered. After Tokugawa Ieyasu moved to Edo, he placed Honda Hirotaka in charge of Shiroi Castle as an important base to control Sanada Masayuki in Numata. The castle was improved by Honda and the stonework and masugata you see today dates from this time period. After the Battle of Sekigahara, the Shiroi Domain was established and several different daimyo controlled the domain until it was ended in 1624.

Visit Notes

This site had been on my radar for a long time, but if I had known how great it was I surely would have gone sooner.

Shiroi Castle is well known for the Shiroi-juku post town running alongside it. The castle was actually abandoned in 1624 but the post town prospered throughout the Edo Period. The street has a nice waterway down the middle but nothing seemed to be open and I did not want to spend much time in between bouts of rain so I moved on to the castle. If you follow the signs from the post town area you first run into the main feature of this castle which is a giant crescent shaped dry moat/trench. Along the outside of this trench is a narrow "obi-kuruwa" or "belt bailey" running most of the length of the crescent.

Following along the bottom of the crescent trench will take you up to the honmaru entrance which is a masugata with some stonework remnants and earthen embankments around the honmaru. You should notice here that it is not just a masugata entrance but there is a narrow "earth bridge" leading into the masugata with the trenches on either side. In the honmaru I do suggest you go to the back of the Honmaru and use the path to the top of the embankment to walk this edge around the Honmaru for better views of the masugata and embankments. In the back of the Honmaru is also a small sub bailey called the Sasakuruwa.

After the Honmaru the Ninomaru, Sannomaru, and Kitakuruwa baileys are all farmland or houses today, but they have some small stone pillars to mark the boundaries. At the entrance to the Kitakuruwa Bailey is a large hill with a little temple on top. This was likely a watchtower/yagura location.

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  • Obikuruwa Bailey
  • Honmaru
  • Sasa Bailey
  • Honmaru Embankment
  • Honmaru Bailey
  • Ninomaru Bailey
  • Ninomaru Bailey
  • Sannomaru Trench
  • Sannomaru Bailey
  • Kita Bailey
  • Kita Bailey
  • Possible yaguradai, watchtower foundation

Castle Profile
English Name Shiroi Castle
Japanese Name 白井城
Founder Nagao Kagenaka
Year Founded 1429-1441
Castle Type Flatland
Castle Condition Ruins only
Designations Local Historic Site
Historical Period Pre Edo Period
Features trenches, castle town
Visitor Information
Access Shibukawa Sta. (JR Joetsu Line); 40 mins walk (there are some infrequent busses too)
Visitor Information park, open any time
Time Required 60 mins
Location Shibukawa, Gunma Prefecture
Coordinates 36° 30' 32.40" N, 139° 0' 38.16" E
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Added to Jcastle 2022
Contributor Eric
Admin Year Visited 2021
Admin Visits June 13, 2021
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