Katsuragaoka chashi-ato, Ainu fortification ruins in Abashiri, Japan

Katsuragaoka chashi-ato is a chashi site on a hill in Katsuragaoka Park, Abashiri, Hokkaido. It consists of two enclosures, one large and one small, with dry moats and three cave dwellings. The main enclosure measures 32.5 metres east-west and 8.4 metres north-south, with a natural cliff to the north and double moats on the other three sides.

The site is a chashi built in the early modern Ainu cultural period, taking advantage of a natural hill. It was designated a National Historic Site on 24 December 1935 and placed under Abashiri City's management on 4 April 1936. Over 520 chashi have been identified in Hokkaido, mostly in the east, and many date largely to the early seventeenth century, possibly linked to increased competition over resources as trade with the Japanese intensified.

The site shows how Ainu communities organized their settlements for both protection and daily life. Open spaces within the fortification reveal where people gathered and carried out common activities.

The site sits within Katsuragaoka Park and is accessible on foot with clear ground-level paths. Information panels scattered throughout explain the construction methods and help visitors understand the layout.

The site also carried two Ainu names: Ishimesinaichashi, "the fort by the stream where dogs bark when they find bears", and Rinnaisanoputsunchashi, "the fort at the mouth of the Abashiri River toward the sea". Three cave dwellings are found at the site, alongside the two dry-moated enclosures.