When Cortés and his Indian allies finally attacked, the Mexica resisted so fiercely despite their weakness that the siege has often been described as the costliest battle in history—casualty estimates range up to 100,000. Absent smallpox, it seems likely that Cortés would have lost. In the event, he was able to take the city only by systematically destroying it. The Alliance capitulated on August 21, 1521. It was the end of an imperial tradition that dated back to Teotihuacan a millennium before.
