Leonardo's work on the cartoon of the Battle of Anghiari was suddenly interrupted in the last months of 1504, and he went to Piombino on a somewhat official mission as a military architect. (During his absence Michelangelo was to receive the commission for the Battle of Cascina.) His mission was preceded by a diplomatic action conducted by Machiavelli himself. It can be inferred, therefore, that it was Machiavelli who suggested Leonardo's name for the programme of fortification projects suggested by Jacopo IV Appiano, Lord of Piombino, an ally of the Florentines at the time of the Pisian war, 1503-4, when Leonardo had already been consulted on the project of diverting the Arno River for strategic reasons, and when Antonio da Sangallo the Elder was the chief military architect of the Florentine Republic. Leonardo's activity at Piombino, revealed by newly discovered evidence, included the study of the city walls, the citadel and the main gate.