 After making an alliance with the Tlaxcalteca, the Spanish went on to conquer the Aztecs.Alvarado commanded one of the eleven vessels in the fleet and also acted as Cortés' second in command during the expedition's first stay in the Aztec capital city of Tenochtitlán.Relations between the Spaniards and their hosts were uneasy, especially given Cortés' repeated insistence that the Aztecs desist from idol worship and human sacrifice; in order to ensure their own safety, the Spaniards took the Aztec king Moctezuma hostage.