It's hardly surprising that CortA©s and his followers should have been so taken by their first sight of TenochtitlA?n , capital of the Aztecs. For what they found, built in the middle of a lake traversed by great causeways, was a beautiful, strictly regulated, stone-built city of 300,000 people, easily the equal of anything they might have experienced in Europe. The Aztec people (or, as they called themselves, the Mexica) had arrived at the lake, after years of wandering and living off what they could scavenge or pillage from settled communities, in around 1345. Their own legends have it that Huitzilopochtli had ordered them to build a city where they found an eagle perched on a cactus devouring a snake, and this they duly saw on an island in the middle of the lake; this is the basis of the nopal, eagle and snake motif that forms the centrepiece of the modern Mexican flag and appears everywhere, from coins and official seals to woven designs on rugs. The reality was probably more desperate - driven from place to place, the lake seemed a last resort - but for whatever reasons it proved an ideal site. Well stocked with fish, it was also fertile, once they had constructed their chinampas , or floating gardens of reeds, and virtually impregnable, too: the causeways, when they were completed, could be flooded and the bridges raised to thwart attacks (or to escape, as the Spanish found to their cost on the Noche Triste ).

The island city eventually grew to cover an area of some thirteen square kilometres, much of it reclaimed from the lake, and from this base the Aztecs were able to begin their programme of expansion: first, dominating the valley by a series of strategic alliances, war and treachery, and finally, in a period of less than a hundred years before the Conquest, establishing an empire that demanded tribute from and traded with the most distant parts of the country