The Siege of Urgench occurred in early 1221 when the Mongol ruler Genghis Khan and his sons laid siege to the Khwarazmian stronghold of Urgench during the Mongol conquest of Khwarazmia.
Following Samarkand's fall in 1220, Shah Muhammad II of Khwarazm fled to the Caspian Sea along with his mother, the ruler of Urgench. This led to Khumar Tegin proclaiming himself "Sultan of Urgench", bracing for the impending Mongol attack. Genghis' eldest son Jochi approached the city from the north, while Genghis and his other sons Chagatai Khan and Ogedei Khan approached the city from the south. The city, built along the Amu Darya in a marshy delta area, was well-defended; the soft gronud did not lend itself to siege warfare, and there was a shortage of large stones for the Mongol catapults.
Jochi attempted to negotiate the city's surrender, angering Chagatai; Genghis headed off this sibling fight by appointing Ogedei to supreme command. The Mongols then attacked, overcoming stout resistance from the garrison and suffering heavy losses to their lack of familiarity with city fighting. The city's artisans were sent back to Mongolia, the young women and children were given to the Mongols as slaves, and Genghis ordered the massacre of the rest of the population by demanding that each of his 50,000 troops execute 24 Urgench citizens each.
If each soldier succeeded, up to 1.2 million people (an exaggerated number) may have been massacred in what is, regardless, one of the bloodiest massacres in human history. The Mongols then broke the dams and flooded the city, destroying old Urgench.