The Spanish forces of Hernan Cortes start their march on Tenochtitlán in December 1520. The capture of the city iin August 1521 marks the fall of the Aztec empire.
Citation:
Editors. "Aztec capital captured by the Spanish and their allies".
The Literary Encyclopedia. First published 01 March 2010
[http://www.litencyc.com/php/stopics.php?rec=true&UID=9945, accessed 18 May 2013.]