Di Giorgio invention described as a weight operated clock bell. 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. Francesco di Giorgio Martini (1439-1501) was an Italian painter of the Sienese School and a sculptor, Quattrocento architect, visionary architectural theorist, and military engineer.