The Aztec city-state of Tenochtitlan began as an island in Lake Texcoco and grew in size and power through warfare and alliances that allowed it to obtain resources and prisoners for sacrifice. In 1446, Montezuma ordered a great embankment to be built to protect the expanding city. A few years later, the Aztecs formed a Triple Alliance with two neighboring cities that continued conquering lands, controlling an empire of four million people by the 16th century when the Spanish arrived. Montezuma, the Aztec emperor, lived luxuriously in a decorated palace and prohibited ordinary people from seeing him at meals.