The Mongol Empire: A Historical Encyclopedia [2 volumes]: A Historical ... - Google Books

https://books.google.de/books?id=4gB9DQAAQBAJ&pg=RA1-PA124&dq=Calendar#v=onepage

In the 13th century, Chinggis Khan rose to power, leading an empire of a million people and defeating surrounding regions with much larger populations. This compendium follows the achievements—and failures—of the Mongol Empire from the birth of Chinggis…