Iimoriyama Castle, Mountain castle ruins in Shijōnawate, Japan

Iimoriyama Castle is a mountain fortress ruin in Shijōnawate, Japan, positioned on a summit at 316 meters elevation. The site covers 1200 meters from north to south and 500 meters from east to west with more than 70 recognizable defense areas.

The fortress became a major power center when warlord Miyoshi Nagayoshi relocated his main base here and controlled the Kinki region and Shikoku from this position. This happened around 1560 after he abandoned his earlier position on Mount Akutagawa.

The name Iimori is not linked to horses in the sources; the castle is also called Iimoriyama Castle. Excavations in the Kuyatsuka enclosure found the remains of a brick-paved building, likely a defensive tower, and a dish called tsukidatezara comparable to examples at Kasuga Taisha in Nara, suggesting a religious facility there. The site was chosen as a Continued Japan Top 100 Castle (No. 160) in 2017 and designated a national Historic Site in October 2021.

Hikers reach the ruins via a trail starting from either Shijōnawate Station or Nozaki Station, taking about 50 minutes to the summit. The path goes through forested terrain with some steep sections, so sturdy shoes are recommended.

Excavations from 2016 to 2018 uncovered large-scale stone walls that the nearby Akutagawa Castle lacked; researchers estimate they predate those of Komakiyama Castle, often called the first castle consolidated with stone walls. A stone-walled path is thought to have led visitors up the east side.