Maymūn-Diz (Persian: میمون دز)[1] was a major fortress of the Nizari Ismailis of the Alamut Period described in historical records.

Recently, Enayatollah Majidi located it on top of Mount Shatan (کوه شاتان Kūh-e Shātān; 36°28′34″N 50°36′25″E / 36.4762463°N 50.6069645°E / 36.4762463; 50.6069645) near Khoshk Chal.

[4][5] The fortress was surrendered by Imam Rukn al-Din Khurshah, who was residing there, to the invading Mongols under Hulagu Khan and was subsequently demolished.

[9] After the Mongol invasion of Iran and the subsequent death of the last Khwarezmian emperor, Hulagu Khan began to conquer the strongholds of the Nizari Ismailis as the main objective.

[10] As winter was approaching, the besieging Mongols faced supply problems due to the difficulty of finding fodder for their horses.