Why did the aztecs built their city there ?

Aztecs were able to settle there because no one else wanted the land.

Explanation:

Aztecs built up islands where they could grow crops. The water also worked as a natural defense against attacks from other cities.

i confess that there are several parts of this constitution which i do not at present approve, but i am not sure i shall never approve them: for having lived long, i have experienced many instances of being obliged by better information or fuller consideration, to change opinions even on important subjects, which i once thought right, but found to be otherwise. it is therefore that the older i grow, the more apt i am to doubt my own judgment, and to pay more respect to the judgment of others.

c) troops march forward in close formation against newer, more accurate weapons