Just at this point of his development, Michelangelo was brought into competition with Lionardo da Vinci, the only living rival worthy of his genius. During the year 1503 Piero Soderini determined to adorn the hall of the Great Council in the Palazzo Vecchio with huge mural frescoes, which should represent scenes in Florentine history. Documents regarding the commencement of these works and the contracts made with the respective artists are unfortunately wanting. But it appears that Da Vinci received a commission for one of the long walls in the autumn of that year. We have items of expenditure on record which show that the Municipality of Florence assigned him the Sala del Papa at S. Maria Novella before February 1504, and were preparing the necessary furniture for the construction of his Cartoon. It seems that he was hard at work upon the 1st of April, receiving fifteen golden florins a month for his labour. The subject which he chose to treat was the battle of Anghiari in 1440, when the Florentine mercenaries entirely routed the troops of Filippo Maria Visconti, led by Niccolò Piccinino, one of the greatest generals of his age. In August 1504 Soderini commissioned Michelangelo to prepare Cartoons for the opposite wall of the great Sala, and assigned to him a workshop in the Hospital of the Dyers at S. Onofrio. A minute of expenditure, under date October 31, 1504, shows that the paper for the Cartoon had been already provided; and Michelangelo continued to work upon it until his call to Rome at the beginning of 1505. Lionardo's battle-piece consisted of two groups on horseback engaged in a fierce struggle for a standard. Michelangelo determined to select a subject which should enable him to display all his power as the supreme draughtsman of the nude. He chose an episode from the war with Pisa, when, on the 28th of July 1364, a band of 400 Florentine soldiers were surprised bathing by Sir John Hawkwood and his English riders. It goes by the name of the Battle of Pisa, though the event really took place at Cascina on the Arno, some six miles above that city.