Leonardo was now approaching other solutions to pure flight when further hostilities interrupted his work. Florence and Pisa were in bitter rivalry, and their struggle had assumed the proportions of a major war. The Florentine army was now practically at the gates of Pisa. Niccolò Machiavelli urged the Signoria to enlist the help of Leonardo da Vinci, who might be able to think of an immediate plan for destroying Pisa and her army. Never one to think in terms of an immediate battle or a temporary success, Leonardo put forth a daring and sweeping plan that would forever reduce the power of Pisa. The plan was as simple as it was monumental—divert the Arno river from its course into two canals that would empty into the sea at Leghorn south of Pisa. In this way, Pisa would lose her water supply and her opening to the sea. The plan met with immediate approval and by the end of July 1503, Leonardo was sent out to survey the entire course of the river. He was accompanied by Giovanni “the Piper,” a man who was frequently employed on minor engineering projects and who was the official player of the pipes to the city of Florence. Giovanni was also the father of Benvenuto Cellini, who became the most famous goldsmith of the Renaissance. As they made their way to Pisa, Leonardo made some more of his extraordinary maps of the area, paying particular attention to the course of the Arno and its tributaries. These maps later inspired him to plan a whole series showing the main watersheds of Italy. When he rode into the Florentine camp drawn up before Pisa, Leonardo designed from his observations and maps, a dam on the Arno to regulate the course of the river. This bird’s-eye view map is a marvel of exactness. It shows the flow of the river hitting the dam with its swirling backwash and overflow. Leonardo’s knowledge of the movement of water was so great and his craftsmanship in drawing so fine that the water in this map seems to flow before one’s eyes. One of the main problems in regulating the Arno was its tendency to continually be shifting its bed by the deposits of new sediment, and Leonardo realized it would be a long time before this project could be completed. When he returned to Florence he presented to the Signoria, as part of his survey, various machines to hasten the excavation of the Arno. He had designed a crane that would assist in the digging out of two different levels at the same time. He also submitted the results of his calculations on the saving of muscular energy by the use of such machines. In addition, Leonardo proposed to use the water in the canals for irrigation purposes and had even calculated what the volume and velocity of a jet of water would be if projected from an opening in the bottom of the canal wall into an irrigation ditch. As if this were not enough, he had invented a practical method of piling as a foundation for the lock-basins to protect them against the dangers of erosion.