After leaving Milan, Leonardo went through a very unstable period, in which he wandered from city to city.

Summoned by Isabella d’Este, who urgently desired to own a work by the artist who, with the Last Supper, had become one of the most acclaimed of his time, Leonardo spent the winter at the Court of Mantua. The next year he went to Venice, probably in the capacity of engineer, to offer his consultation on the best defense system to be adopted against the invasion of the Turks on the Isonzo.

In the summer of 1500 he returned to Florence to verify, along with other engineers, the stability of the church of San Salvatore dell’Osservanza.

During this period Leonardo diligently pursued his studies in geometry and drew a cartoon with a Saint Anne that aroused the fervent admiration of the Florentines who saw it in the Church of the Santissima Annunziata. Another cartoon for a Saint Anne is found in the National Gallery of London, while the panel painted by Leonardo during his last years is now in the Louvre.

In 1502 Leonardo, in the capacity of military engineer, entered the service of Cesare Borgia during his campaign in the Marche and in Romagna. On that occasion Leonardo drew the map of Imola, now in the Windsor Collection. But the dream of a life spent in the field, designing architectural solutions, was destined to conclude within the span of a year; in 1503 Leonardo came back to Florence to live.