Leonardo Fibonacci

Born in Pisa around 1170, Leonardo of Pisa—better known as Fibonacci—was an Italian mathematician whose work helped reshape European mathematics. As the son of a merchant, he traveled in the Mediterranean world and learned the Hindu-Arabic numeral system, which he recognized as more efficient than Roman numerals for calculation.

His best-known book, Liber Abaci (1202), explained how to use these numerals in everyday business, bookkeeping, and problem-solving. That book played a major role in spreading the decimal place-value system in Europe. A problem in Liber Abaci about rabbit population growth later became famous as the Fibonacci sequence, though that was only one small part of his wider mathematical work.

Fibonacci also wrote on geometry and number theory, and his reputation was strong enough that he was honored by the city of Pisa. Today he is remembered not just for a famous sequence, but for helping connect European learning with mathematical ideas that had developed across the broader Mediterranean world.