Order of Assassins or simply Assassins is the common name used to refer to an Islamic sect formally known as the Nizari Ismailis. Based on texts from Alamut, their grand master Hassan-i Sabbah tended to call his disciples Asāsiyyūn (أساسيون, meaning "people who are faithful to the foundation [of the faith]"), but some foreign travellers like Marco Polo misunderstood the name as deriving from the term hashish.
Often described as a secret order led by a mysterious "Old Man of the Mountain", the Nizari Ismailis formed in the late 11th century after a split within Ismailism – a branch of Shia Islam.
The Nizaris posed a strategic threat to Sunni Seljuq authority by capturing and inhabiting several mountain fortresses throughout Persia and later Syria, under the leadership of Hassan-i Sabbah. Asymmetric warfare, psychological warfare, and surgical strikes were often a tactic of the assassins, drawing their opponents into submission rather than risk killing them.
While "Assassins" typically refers to the entire sect, only a group of acolytes known as the fida'i actually engaged in conflict. Lacking their own army, the Nizari relied on these warriors to carry out espionage and assassinations of key enemy figures, and over the course of 300 years successfully killed two caliphs, and many viziers, sultans, and Crusader leaders.
During the rule of Imam Rukn-ud-Din Khurshah, the Nizari state declined internally, and was eventually destroyed as the Imam surrendered the castles to the invading Mongols. The Mongols destroyed and eliminated their Order. Mentions of Assassins were preserved within European sources – such as the writings of Marco Polo – where they are depicted as trained killers, responsible for the systematic elimination of opposing figures. The word "assassin" has been used ever since to describe a hired or professional killer, leading to the related term "assassination", which denotes any action involving murder of a high-profile target for political reasons.
The Nizari were acknowledged and feared by the Crusaders. The stories of the Assassins were further embellished by Marco Polo. European orientalist historians in the 19th century – such as Joseph von Hammer-Purgstall – also referred to the Nizari in their works and tended to write about the Nizari based on accounts by medieval Sunni Arab and Persian authors.