Pope Sylvester II (b. 946)
Pope Sylvester II (c.  946 – 12 May 1003), originally known as Gerbert of Aurillac, was a French-born scholar and teacher who served as the bishop of Rome and ruled the Papal States from 999 to his death. He endorsed and promoted study of Arab and Greco-Roman arithmetic, mathematics and astronomy, reintroducing to Europe the abacus and armillary sphere, which had been lost to Latin Europe since the end of the Greco-Roman era. He is said to be the first to introduce in Europe the decimal numeral system using the Hindu-Arabic numeral system. He is credited with the invention of the first mechanical clock in 996.