Galileo Galilei, the founder of modern physics, was born near the Arno River in Pisa (a Roman colony of the second century B.C., conquered by Florence in 1405), on 15 February 1564 when Cosimo de' Medici (1519-74) the Great (not Cosimo I, the Elder, (1389-1464) who founded the Medici dynasty), was Duke of Florence (first Grand Duke of Tuscany as of 1569).