States People Centers Other Lambsar (Persian: لمبسر, also pronounced Lamsar), Lamasar, Lambasar, Lambesar (لمبه سر) or Lomasar (لمسر)[1] was probably the largest and the most fortified of the Ismaili castles.

The fortress is located in the central Alborz mountains, south of the Caspian Sea, about 120 km from present-day Tehran, Iran.

Kiya Buzurg Ummid (died 1138) captured the castle from Rasamuj and rebuilt it into a major stronghold using local labour.

The huge two-layered parapets made up of very large 10m high stones, along with the main building in the north of the fortress with 1.2m wide cut stone walls, wonderful water reservoirs and grain stores in the south and southeast of the castle, towers and a water supply system are among the characteristics and features left within the Lambsar fortress which intrigue visitors.

In 1256 AD after a couple months the Meymoon-Dej (Meymoon-Diž, Persian: میمون دژ) fort surrendered to Hulaku’s army, and Imam Rukn ad-Din Khurshah was captured.