Aterazawa Tateyama Castle, Mountain fortress site in Ōe, Yamagata Prefecture, Japan

Aterazawa Tateyama Castle occupied a U-shaped plateau about 100 meters above a bend of the Mogami River near its confluence with the Sagae River. The site measures roughly 500 meters long and up to 400 meters wide, divided into small terraces by clay walls, with vertical dry moats on the river-facing slope. Only fragments of earthen ramparts and moats remain.

The Aterazawa family built the first fortifications here in the 14th century to control river passage and trade. Their power ended in 1584 when they were defeated by the rival Mogami clan.

This was the seat of the Aterazawa family, who held power in the region during medieval times. Today visitors walk through grounds where local families once controlled river passage and regional trade routes.

The ruins lie in Tateyama Park, about 25 minutes on foot from JR Aterazawa Station, or 8.5 km (20 minutes by car) from the Sagae interchange. The main approach climbs to the honmaru and ninomaru, whose summit terrace, the Senjōjiki, is flat and open. The sannomaru is cut off by a dry moat that once carried the road to Sagae, Yachi and Ōishida.

Vertical dry moats were cut into the slope facing the Mogami River to stop attackers climbing up from ships anchored below the castle. The site also preserves traces of a small masugata-style gate at the entrance and earthen ramparts on the hill behind.