Pacioli, Luca (c. 1445 - 1517)

A native of Borgo Sansepolcro. In 1500 Leonardo returned to Florence accompanied by Luca Pacioli, who stayed as guest in the Franciscan monastery of Santa Croce. Leonardo had met the illustrious mathematician in Milan, where he had been his pupil during the years when he was illustrating the De Divina Proportione. Of this work, finished in 1498, three manuscript copies were compiled: the first is now in the Geneva Civic Library, the second in the Milan Ambrosian Library, and the third has been lost.
Pacioli recalled, among other things, in the De Viribus Quantitis, a manuscript from 1496 now at the University of Bologna Library, an emergency bridge made by Leonardo, "noble engineer of Cesare Borgia, Duke of Romagna and Lord of Piombino", without «either iron bars or ropes», to allow an army to cross a river.