Lambsar (Persian: لمبسر, also pronounced Lamsar), Lamasar, Lambasar, Lambesar (لمبه سر) or Lomasar (لمسر) was probably the largest and the most fortified of the Ismaili castles. The fortress is located in the central Alburz mountains, south of the Caspian Sea, about 120 km from present-day Tehran, Iran. Lambsar is to the northeast of Razmian village (the central district of Roodbar e Shahrestan). Kiya Buzurg Ummid (died 1138) captured the castle from Rasamuj and rebuilt it into a major stronghold using local labour. He was appointed by Hassan-i Sabbah (died 1124) as its governor.