In 1202, Fibonacci (a.k.a. Leonardo of Pisa) published Liber abaci ("book of the abacus"), the first European books to use decimal notation in arithmetic (which Fibonacci learned in his native North Africa). The spread of decimal arithmetic made possible the great "Age of Navigation" and "Age of Trading", which followed -- although historians choose to ignore this.

Can you imagine trying to balance your bankbook or fill your tax statement with Roman numerals? In Fibonacci's time, the University of Bologna was the only place in the world which taught the best methods for dividing with Roman numerals.