|Town or city||Razmian|
| Part of a series on Shīʿī Islam
Lambsar (Persian: لمبسر, also pronounced Lamsar), Lambasar, or Lambesar (لمبه سر) was probably the largest and the most fortified castles of the Nizari Ismaili state. The fortress is located in the central Alburz mountains, south of the Caspian Sea, about 120 km from present-day Tehran, Iran. Lambesar is to the northeast of Razmian village (the central district of Roodbar e Shahrestan).
Only ruins remain of this magnificent fortress today. Very deep valleys surrounding the fortress make it impossible to access from the East and West sides. The North and South fronts are the only possible ways to get into the fortress. Although the slope of the mountain with a difference of 150m on both levels is stretched from north to south with a length of 480m, the castle is more than 190m in width. 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 Lambesar fortress which intrigue visitors. In the North side of the fortress a huge building with 4 smaller extensions remain which face to the East.
Final days of Lambesar
The Ismailis’ forts were the last line of defense against Mongol aggression in Persia. The Mongols had a hard time conquering Ismailian's forts. Hulaku Khan was disappointed with his commanders therefore he took over an army of 10000 soldiers and moved toward Alamut. In 1256 AD after a couple months the Meymoon-Dej (Meymoon-Diž, Persian: میمون دژ) fort surrendered to Hulaku’s army, and Imam Rukn-ud-Din Khurshah was captured. Hulaku Khan asked Rukn-ud-Din Khurshah to order his followers to surrender, but Lambesar fort, Gerdkuh fort and Alamut fort did not follow the order. Finally after a year of resisting, a cholera epidemic in 1257 AD took many lives in Lambesar and allowed the Mongols to succeed. Hulaku ordered the fort ruined and beheaded whoever had survived the deadly disease. In 1275 AD and again in 1389 AD, small groups of Ismailis who had survived the Mongol invasions attempted to recapture Alamut, but their attempts were short-lived.
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