Cortes Besieges Tenochtitlan
Custom-built warships, a cut aqueduct, and tens of thousands of Tlaxcalan allies grind down a starving, plague-weakened capital
Quick facts
- Siege began
- April 1521
- Spanish force
- c. 700 infantry, 86 horses, 18 field guns
- Indigenous allies
- At least 100,000 Tlaxcalans
- Key tactic
- 13 brigantines, aqueduct cut May 26
What happened
Cortes began his siege of Tenochtitlan in April 1521 with a force World History Encyclopedia records as 700 infantry, 118 crossbowmen and gunners, 86 horses, and 18 field guns, but the decisive numerical advantage came from at least 100,000 Tlaxcalan allies fighting alongside the Spanish against their old Aztec enemies. On April 28, Cortes launched 13 specially built brigantines onto Lake Texcoco, prefabricated ships that could contest the Aztecs' vast fleet of war canoes in a way nothing before had. On May 26, Pedro de Alvarado's forces destroyed the Chapultepec aqueduct, cutting off Tenochtitlan's supply of fresh water and forcing the city to rely on brackish lake water. Through May and June, three Spanish columns pushed into the city from the west, south, and east while the brigantines blocked the causeways, and Cortes's own force was nearly captured during a failed assault on June 30, saved only by the Aztec preference for taking live captives rather than killing enemies outright in the field.
Why it matters
This siege combined every advantage the Spanish had built over two years: European ships never before seen on the lake, a coalition of tens of thousands of indigenous allies drawn from decades of Aztec Flower War resentment, and a population inside the city already devastated by smallpox and starvation before a shot was fired. The city's defenders, led by the new ruler Cuauhtemoc, fought with genuine skill and adapted their tactics to European weapons, but could not overcome all three disadvantages at once.
How we know
The siege is documented in extensive detail by the conquistador Bernal Diaz del Castillo's firsthand memoir The Conquest of New Spain, cross-checked against Nahua accounts recorded later in works like the Florentine Codex.
Sources
- World History Encyclopedia. The Fall of Tenochtitlan · Reputable sourceworldhistory.org · The domain "worldhistory.org" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- World History Encyclopedia. The Fall of Tenochtitlan · Reputable sourceworldhistory.org · The domain "worldhistory.org" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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Part of a timelineThe Aztec Empire25 events · From a wandering clan on a swampy island to the dominant power of Mesoamerica, and its end in a 93-day siegeView all →