Color enhanced pen-and-ink drawing showing 15th-century Italian designs for underwater breathing apparatus for divers. From "Della providentia della chuera," by Francesco di Giorgio Martini of Siena (1439-1502). Between the Middle Ages and the Renaissance, Siena developed a series of technical specialities. Siena's artist-engineers put their skills into practice for their small republic and demonstrated their skill in depicting machines and mechanical systems. The two most prominent Sienese engineers were Mariano di Iacopo, known as Taccola, and Francesco di Giorgio.