The siege of Gurganj occurred during the Mongol invasion of the Khwarazmian Empire. The siege's length is variable, with historians such as Rashid al-Din Hamadani stating that it lasted for seven months, but it is largely agreed that it ended with the defeat and annihilation of the city in April 1221. Genghis Khan, ruler of the Mongol Empire, had launched a multi-pronged assault on the Turkic Khwarazmian Empire, ruled by Shah Muhammad II. Through a combination of efficient planning and excellent manoeuvering, the Khan's army managed to take the border town of Otrar swiftly, followed by the large cities of Bukhara and Samarkand. The siege, among others, was witnessed by the Persian biographer Shihab al-Din Muhammad al-Nasawi, who recorded an account in Arabic c. 1241.