The pope invented a brand-new title for Cosimo de' Medici, and emperors fumed
In 1569 Pope Pius V declared Cosimo de' Medici Grand Duke of Tuscany, a rank nobody in Italy had held before. The Holy Roman Emperor and the King of Spain were furious, insisting Florence was an imperial fief. It took six years and 100,000 ducats before the emperor finally accepted the new title.
By then Cosimo had ruled Florence for 32 years. He had bought Elba from Genoa in 1548 and fortified a naval base there, conquered Siena in 1555, barred clergy from administrative jobs and passed religious freedom laws unusual for his age. The papal bull of 27 August 1569 rewarded his long support for Pius V. Emperor Maximilian II and Philip II of Spain called it invalid, and even Catherine de' Medici, Queen of France, looked on him with scorn. Maximilian relented in 1575 for Cosimo's son Francesco, who had to pay the imperial treasury, and Spain followed in 1576.
Cosimo's reign was among the most warlike in Tuscan history, including a part in the Holy League that beat the Ottomans at Lepanto in 1571. Plague killed his wife, Eleanor of Toledo, and four of their children in 1562, and grief and illness led him to hand power informally to Francesco in 1564. Francesco preferred scientific experiments to government and is chiefly remembered because he and his second wife, Bianca Cappello, died on one and the same day, which fuelled rumours of poison.
His brother Ferdinando, whom he detested, proved far more energetic. He drained marshes, built roads in southern Tuscany, promoted trade at Livorno and lined highways with mulberry trees to feed silkworms. He tilted away from the Habsburgs by marrying Christina of Lorraine and wed his niece Marie to Henry IV of France, and even backed a Tuscan colony near modern French Guiana. Still, Florence had only about 75,000 people at the start of the 17th century, well behind Rome, Milan or Naples.
Decline set in under Ferdinando II and Cosimo III, and the senior Medici line died out in 1737. Francis Stephen of Lorraine inherited the throne. After a Napoleonic interlude as the Kingdom of Etruria and French annexation, the grand duchy returned in 1814, then voted by 95 percent to join the Kingdom of Italy in 1860.
Source: Grand Duchy of Tuscany
