The word assassin is derived from the Arabic word Hashshashin (Arabic: حشاشون \ جماعة الحشاشين), referred to the Persian designation of the Nizari branch of the Ismā’īlī Shia under the instruction of Hassan aṣ-Ṣabbaḥ during the Middle Ages. They were active in the fort of Alamut in Iran from the eighth to the fourteenth centuries. This group killed members of the Arab Abbasid, Seljuq and crusaders élite for political and religious reasons, but mostly targeted the knights Templar and the ruling Fatimid Sunni kings.
Although commonly believed that assassins were under the influence of opium during their killings or during their indoctrination, there is continued debate within the historical community whether these claims have any merit, as direct evidence from any contemporary source, Nizari or otherwise, is non-existent. Marco Polo and subsequent European visitors to the area received from rivals of the Nizarai, what were to these opponents, derogatory names for the Nizarai Ismaili, and significantly embroidered stories about them. Polo, Henry II, Count of Champagne, William Marsden, an envoy of Frederick Barbarossa, William, Archbishop of Tyre and others following, popularized the names and stories in Europe, oblivious to their origin in factional propaganda.
The earliest known literary use of the word assassination is in Macbeth by William Shakespeare.