Ono Castle, also called Miyayama Castle, was located at the top of Mt. Seikai in Tokoname City, Aichi Prefecture. The castle was resided first by the Ono clan, the descendant of the Owari-Genji family, then the Isshiki clan, and finally the four generations of the Saji clan.

The Saji clan built up Chita Suigun (the naval forces) and played an important role in promoting maritime trade and controlling marine transportation in Ise Bay. Oda Nobunaga and Toyotomi Hideyoshi placed great importance on their naval power and Nobunaga’s sister and niece were married off to the Saji clan.

Nobunaga’s niece, Ogo (or Oeyo), whose mother is Nobunaga’s sister Oichi, was married to Saji Kazunari, the 4th head of the Saji clan, by the order of Hideyoshi. However, when Kazunari sided with the Tokugawa and Oda allied forces later, Hideyoshi got angry and made the couple get divorced in 1584. Later in 1595, she remarried Tokugawa Hidetada, the 3rd son of Ieyasu and later the 2nd Tokugawa Shogun, and became the mother of his successor, Iemitsu.

The castle ruins site has been arranged into the park, where the two-story donjon and the castle gate were newly constructed. You can command a wonderful view of Ise Bay from the observatory deck on the donjon. The Saji clan is enshrined at Saji Shrine in the ruins site of the watch tower.