A large Imperial and Spanish army under Philibert of Châlon, Prince of Orange and Pier Maria III de' Rossi[1] surrounded the city and after a siege of nearly ten months, captured it.

After the capture of Volterra by the Imperial forces and the death of Francesco Ferruccio at the Battle of Gavinana, further resistance became impractical, and the city surrendered in August 1530.

At the conclusion of the Treaty of Bologna in the summer of 1529, Charles and Clement, the father of Alessandro de' Medici began to plan an offensive against the Florentine Republic.

The Prince of Orange arrived in Rome at the end of July; there, he was given some 30,000 ducats (with promises of additional funds later) by the Pope, and ordered to attack Perugia (which was held by Malatesta Baglioni) and Florence.

[2] The Prince of Orange was able to collect some 7,000 infantry, mostly the remnants of the landsknechts which had followed Georg Frundsberg into Italy in 1526 as well as various Italian companies no longer employed due to the denouement of the war.

[8] Viewing the Florentine earthworks too substantial to easily take by assault, the Imperial army settled into a pattern of artillery duels and skirmishing with the defenders instead.

[9] Meanwhile, the lack of fighting in other portions of Italy drew thousands of unemployed soldiers to the Imperial army, substantially swelling its ranks; the new arrivals included Fabrizio Maramaldo, whose reputation for brutality was such that even Clement opposed allowing him to take part in the siege.

[12] With the loss of Volterra, Florentine hopes of opening a supply line into the city dwindled, and Florence looked to the arrival of Ferruccio with a relief army, which he had gathered around Pisa.

The Prince of Orange, having arranged that Baglioni would not attack the Imperial forces in his absence, marched out with the larger portion of his army to intercept him.