In 1256, the Mongol army under Hulagu Khan marched on the mountain fortress of Alamut, stronghold of the Nizari Ismaili state—better known in the West as the Assassins. For decades, the Nizari had used strategic assassinations to wield influence far beyond their numbers, targeting caliphs, viziers, and even Crusader leaders. But faced with the Mongol war machine, their distant castles and secret tactics proved no match. Hulagu demanded submission; the Nizari Grand Master Rukn al-Din Khurshah hesitated, negotiated, and ultimately surrendered, only to meet a violent end. The fall of Alamut marked the destruction of a unique state and the looting of its legendary library, which contained priceless Ismaili manuscripts—most of which were lost forever. This episode explores the siege itself, the strategic thinking behind the Mongol campaign, and the legacy of the Assassins, drawing on Persian chroniclers like Juvayni and Rashid al-Din. We also discuss how the Mongols absorbed Nizari expertise, including their network of informants, and what the episode reveals about Mongol statecraft: systematic destruction paired with pragmatic co-option.