[1] The second Duke, Cosimo I, established a strong Florentine navy and expanded his territory, purchasing Elba and conquering Siena.

In April 1532, the Pope convinced the Balía, Florence's ruling commission, to draw up a new constitution, which formally created a hereditary monarchy.

Alessandro continued to rule Florence for another two years until he was murdered on 1 January 1537 by his distant relative Lorenzino de' Medici.

[9] At the news of this, the exiled Strozzi family invaded and tried to depose Cosimo, but were defeated at Montemurlo.

In alliance with Spain and the Holy Roman Empire, Cosimo defeated the Republic of Siena, which was allied with France, in the Battle of Marciano on 2 August 1554.