The manuscripts by 15th-century Italian engineers show their attempts to apply the concept of perpetual motion to operating machines. In his De ingeneis, the Sienese Mariano di Jacopo, known as Taccola (1381-ca. 1458), describes the overbalanced wheel with articulated arms depicted by Honnecourt and in Arab manuscripts. He also provides diagrams of overbalanced wheels and of what appears to be a wheel with moving arms and buckets for excavation. Another Sienese engineer, Francesco di Giorgio (1439-1501), explores the topic of a recirculation mill. He draws a hydraulic motor connected to a piston pump or an Archimedes’ screw that was supposed to be powered by the force of the falling water raised by the motor itself.