Why did Tenochtitlan impress the Spanish?

The Spaniards were very much amazed by the sight of Tenochtitlan, they could never have pictured that the Americas held one of the biggest metropolitan areas in the known world, with almost five thousand buildings within a 13 square kilometers of swampy islands, 80,000 homes and two markets with forty four thousand daily attendants on one of just the four causeways linking islands to the mainland, where people would sell gold, jewels, copper, fabrics among more goods.

Hernan Cortez himself stated it best in one of his letters about the time he laid eyes at what was once Mesoamerica:

>This Great City of Temixtitan stands in the middle of this salt lake, and from the mainland to the city, are four leagues, by ways raised two lances in lenght and eight paces across. And they are very well constructed, as wide as two horsemen with lances can ride abrebreast, and with good walls on both sides, and so high the bridges they have between two stretches are made like drawbridges, which can be removed whenever people wish to take them away from anyone coming by land because this great city in built in the water cannot in anyway be taken except in this fashion.[Hernan Cortez- Letters.]