 When Cortés returned to Tenochtitlan, he found the Spanish force under siege.After Moctezuma was killed in the attempt to negotiate with his own people, the Spaniards determined to escape by fighting their way across one of the causeways that led from the city across the lake and to the mainland.In a bloody nocturnal action of 10 July 1520, known as La Noche Triste, Alvarado led the rear-guard and was badly wounded.