Answer:
Hernán Cortés arrived at what is now Veracruz with an army of approximately five hundred Spaniards. When he entered Tenochtitlán, what is now Mexico City, about half of his army had been lost in various skirmishes and were replaced by an equivalent number of conscripts sent by the governor of Cuba to kill him; he was accompanied at that time by several thousand (the count is unclear, most likely between two thousand and five thousand) native warriors drawn from the eastern provinces of the Mexica (also called "Aztec") empire.
Cortés was always vastly outnumbered. Tenochtitlán was larger than any city in Europe at that time. Even today, for that matter.
The best eyewitness account is that of Bernal Díaz de León, La verdadera historia de la conquista de Nueva España, which is also available in a good English translation.
Explanation: