Tenochtitlan is the capital of the Aztec civilization, it was located where modern day Mexico City rests. The Montezuma campaign in Age of Empires II: The Conquerors is focused around this city and its invaders, the Spanish. In the second-last Scenario in the Campaign you fight to regain control of the city, and in the last Scenario you control Tenochtitlan, using its resources and buildings to gain an economic advantage, while at the same time you are:
1. Repelling attacks from your Tlaxcallan enemies, as well as from the Spanish army and their navy, and
2. Attacking and hopefully destroying your enemies.