The Order of Assassins
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A lengthy and very interesting! article about "agents of the medieval Nizari Ismaili, a faction of Shiite Muslims who broke away from the larger Shiite community in the late 11th century. They took refuge in an assortment of castles in the mountains of Syria and what is now Iran."
"For nearly two centuries, from the late 11th to the mid-13th centuries, the Order of Assassins inspired fear and respect from rulers with big, powerful armies. Their fighters, who became known in Western legend as the Assassins, generally avoided battles altogether. Instead, they almost entirely relied upon surprising and killing leaders of their enemies."
Lots more: https://history.howstuffworks.com/world-history/order-of-assassins.htm
Not to mention, the phrase "assortment of castles" tickles me.
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https://www.etymonline.com/word/assassin
1530s (in Anglo-Latin from mid-13c.), via medieval French and Italian Assissini, Assassini, from Arabic hashīshīn (12c.), an Arabic nickname, variously explained, for the Nizari Ismaili sect in the Middle East during the Crusades, plural of hashishiyy, from the source of hashish (q.v.).
They were a fanatical Muslim sect in the mountains of Lebanon at the time of the Crusades, under leadership of the "Old Man of the Mountains" (which translates Arabic shaik-al-jibal, name applied to Hasan ibu-al-Sabbah). In Western European minds 12c.-13c. they had a reputation for murdering opposing leaders after intoxicating themselves by eating hashish, but there is no evidence that the medieval Ismailis used hashish.
The plural suffix -in was mistaken in Europe for part of the word (compare Bedouin). Middle English had the word as hassais (mid-14c.), from Old French hassasis, assasis, which is from the Arabic word.