Leonardo Pisano is best know for Fibonacci numbers in math. The sequence is obtained by adding the two previous numbers in the sequence to obtain the next number. The sequence starts 1, 1, 2, 3, 5, 8, 13, etc… Leonardo and his father went to Bugia in North Africa where Leonardo’s father was sent to be a customs official for the merchants of Pisa. It was there that Leonardo learned the Arabic number system. In 1202 he wrote a book describing the system which uses our modern numbering system instead of the Roman numerals which were still used in Europe.  Multiplication and other mathematical computations were difficult using Roman numerals and merchants and bankers in Europe quickly saw the advantage of the new system and it was quickly adopted.

(The Great Courses – Turning Points in Medieval History)