Siege of Tenochtitlan (1521): The Fall of the Aztec Capital

In the spring of 1521 one of the largest cities in the world stood on an island in a highland lake, its temples and palaces joined to the shore by long causeways. By August it was rubble. The fall of Tenochtitlan is often told as the story of a few hundred Spaniards toppling an empire. The historians of Mexico's own institutions tell a larger and grimmer story: a war fought mostly by Indigenous armies against the Mexica who had ruled them, decided as much by disease and hunger as by steel, and ending in one of the most devastating losses of life in the history of the Americas.³

Background: the city on the lake

Tenochtitlan was the capital of the Mexica, the people better known as the Aztecs, and the center of an empire that, at the start of the sixteenth century, drew tribute from some 400 to 500 subject states. It was built on islands in Lake Texcoco, on artificial platforms and fields of chinampas crossed by canals, and fed with fresh water by aqueducts from the springs of Chapultepec. The historian Carlos Brokmann, writing for the National Autonomous University of Mexico, puts its population at between 200,000 and 400,000; National Geographic gives 250,000.⁴

In 1519 Hernán Cortés, sent from Cuba to explore the coast, landed with some 500 soldiers and about 100 sailors and turned the expedition into a war of conquest. A young Indigenous woman, Malintzin, known to the Spaniards as Doña Marina, became his interpreter. On the march inland he won over peoples who resented Mexica rule: the Totonacs of Cempoala and, after hard fighting, the Tlaxcalans, old enemies of the Mexica. At Cholula his army massacred thousands of people.⁵

Moctezuma II let the Spaniards into Tenochtitlan in November 1519 and was soon their prisoner. In 1520, while Cortés was away fighting a Spanish force sent to arrest him, his lieutenant Pedro de Alvarado massacred Mexica nobles and warriors at a religious festival, and the city rose. Moctezuma died in the fighting; by one account his own people pelted him with stones, while the archaeologist Eduardo Matos Moctezuma, of Mexico's National Institute of Anthropology and History (INAH), inclines to the view that the Spaniards killed him. On the night of 30 June 1520, under the new ruler Cuitláhuac, the Mexica drove the Spaniards and their allies out of the city along the causeways with heavy losses, the night the Spaniards called the Noche Triste, the Sad Night.⁶

Armies and commanders

The disaster did not end the war. Cortés retreated to Tlaxcala and rebuilt his army there over the following months. Then disease did what the Mexica army had prevented: smallpox, brought by the Europeans, spread through Tenochtitlan in late 1520. Britannica says it killed half of the city's inhabitants; Cuitláhuac himself died of it after a few weeks on the throne. The young Cuauhtémoc became the last tlatoani, or ruler, of the Mexica.⁷

The Mexica remembered the epidemic in their own words. Book XII of the Florentine Codex, compiled in Nahuatl by the Franciscan Bernardino de Sahagún with Indigenous collaborators who had lived through the conquest, describes victims covered with sores who could no longer move in their beds, and many who died not of the disease but of hunger, because there was no one left to care for them.⁸

The army that came back in 1521 was overwhelmingly Indigenous. Brokmann counts between 200,000 and 300,000 warriors of the allied peoples, among them Tlaxcala, Texcoco, Huexotzinco and Cempoala, supported, in his words, in a limited but significant way by about 1,500 Spaniards. National Geographic gives just under 1,000 Spaniards and 50,000 Indigenous warriors, and Britannica more than 800 Spaniards and tens of thousands of Indigenous fighters. Cortés also had thirteen small brigantines built in pieces, carried overland from Tlaxcala and launched on the lake, to give him command of the water.⁹

The battle in phases

Isolating the city. Before the siege began, Brokmann writes, Tlaxcalans, Huexotzincas and Spaniards raided the towns of the Valley of Mexico and the lands beyond, destroying anything the Mexica could use, with massacres and the mass enslavement of the people. National Geographic describes the same campaign of brutally crushed resistance and branded captives. In May 1521 the attackers seized the aqueduct of Chapultepec and cut off Tenochtitlan's fresh water.¹⁰

The siege. Britannica dates the siege from 22 May; it lasted 93 days, a figure INAH also gives. The besiegers pushed along the causeways under cover of the brigantines, while the Mexica broke the causeways, cut the bridges, blocked the canals against the boats and turned every square and house into a strongpoint. To advance, the attackers burned and demolished houses and filled the canals with the rubble, so that the city was destroyed street by street as it was taken.¹¹

The Mexica counterstroke. The defenders came close to breaking the siege. In one assault the Mexica routed a Spanish column inside the city; Cortés, wounded in the leg, was nearly carried off alive. In his own report to the emperor he counted thirty-five or forty Spaniards and more than a thousand of his Indigenous allies killed that day, and he described how the Spaniards captured alive were sacrificed on the temples of Tlatelolco in sight of their comrades. National Geographic records that the Mexica then won back lost ground and put the Spaniards on the defensive for nearly three weeks.¹²

Turning point

The blockade won in the end. With the water cut, the lake commanded by the brigantines and the allied armies on every causeway, famine took hold in the city, and Cortés's translator and editor Francis MacNutt wrote that it claimed as many victims as the Spanish cannon. The last defenders were driven into Tlatelolco, the twin city in the north of the island, where INAH places the final Mexica resistance.¹³

On 13 August 1521 Cuauhtémoc left the city in a fleet of canoes and was taken on the lake by a Spanish brigantine. What he was doing is disputed. In Brokmann's reading, the Indigenous sources say that the ruler, his wife and the leading nobles were on their way to surrender formally; the Spanish narrative, which Britannica follows, says they were trying to escape. Brokmann argues that the difference mattered, because a surrender would have obliged the Spaniards, under their own laws of war, to stop the killing and the looting.¹⁴

Aftermath

It did not stop. Brokmann describes the days after the fall as a time of general sack, massacre and the enslavement of the survivors, carried out above all by the allied Indigenous armies, as was the custom in Mesoamerica when a city fought to the end, but with the Spaniards taking part. Britannica likewise describes the victors killing indiscriminately, burning houses and destroying temples.¹⁵

No one counted the dead. Cortés himself estimated that 67,000 Mexica fell in the last assaults on the city and 50,000 died of hunger and disease, a figure Matos Moctezuma notes was raised further by later chroniclers. National Geographic gives as many as 100,000 Aztec dead during the siege, against about 100 Spaniards.¹⁶

Cuauhtémoc, the last ruler of independent Tenochtitlan, did not survive the conquest for long. He was kept a prisoner and later hanged by the Spaniards. In his letter to the emperor, Cortés claimed that Cuauhtémoc and another captive lord had been plotting a rising against him on the march to Honduras. Francis MacNutt, who translated the letters in 1908, found no discoverable justification for the execution and called it the blackest deed of Cortés's life.¹⁷

Brokmann stresses that the Indigenous allies saw themselves as the true victors. For every Spaniard there had been 200 or 300 Indigenous warriors, and from their point of view the Triple Alliance had been beaten by its Mesoamerican enemies with some help from the Spaniards. They expected a new order of alliances and tribute of the kind Mesoamerica had always known. Instead, within a few decades, the Spanish colonial order of New Spain swept that world away. Mexico City was built on the ruins of Tenochtitlan.¹⁸

Legacy and memory

Matos Moctezuma explains the fall by four factors together: the psychological shock of omens and the unknown, disease, the economics of an empire built on tribute that left its subjects ready to rebel, and the military. Brokmann's research puts the Indigenous allies at the center of the story and the Spaniards at its edges.¹⁹

In 2021, the 500th anniversary, the Mexican government marked 13 August not as a conquest but as 500 years of Indigenous resistance. President Andrés Manuel López Obrador called it a day of mourning and asked forgiveness of the victims of what he called the catastrophe of the Spanish military occupation of Mesoamerica; the news agency EFE reported that the reframing was controversial and risked reopening old wounds. Like the conquest of the Inca empire that began at Cajamarca a decade later, the fall of Tenochtitlan remains one of the most argued-over events in the history of the Americas.²⁰

Visiting today

Tenochtitlan lies under the center of Mexico City. Its twin, Tlatelolco, where the Mexica made their last stand, survives as an archaeological zone beside the colonial church of Santiago in the Plaza of the Three Cultures. INAH has excavated there since 1944, and on 13 August 2025 it opened a permanent photographic exhibition about the site to mark the anniversary of the Mexica resistance.²¹