Mattias de' Medici

Mattias de' Medici
Portrait of Mattias de' Medici by Justus Sustermans
Governor of Siena
Predecessor	Leopoldo de' Medici
Successor	Francesco Maria de' Medici
Born	(1613-05-09)9 May 1613 Florence, Tuscany
Died	11 October 1667(1667-10-11) (aged 54) Siena, Tuscany
Burial	The Basilica of San Lorenzo
Grand Ducal	House of Medici
Father	Cosimo II de' Medici, Grand Duke of Tuscany
Mother	Maria Maddalena of Austria
Religion	Roman Catholicism

Mattias de' Medici (9 May 1613 – 11 October 1667) was the third son of Grand Duke Cosimo II de' Medici of Tuscany and Archduchess Maria Maddalena of Austria. He was governor of Siena, with interruptions, from 1629. He never married.

Mattias pursued an ecclesiastical career, like his brother Gian Carlo, but found it was not to his liking. Instead, he embarked on a military career at the age of 16. His father, Cosimo II, died on 28 February 1621; he was succeeded by Ferdinando de' Medici, the elder son. On 29 May 1629, Grand Duke Ferdinando appointed Mattias governor of Siena, following the death of their aunt and the then governor, Catherine de' Medici.

He arrived in his domain on 27 August and took up residence in the Piazza del Duomo. Spending the bulk of his time in Siena, he was immensely popular among the Sienese. In 1631, he joined the Austrian belligerency in the Thirty Years' War. He took part in the famous battle of Lützen, in October 1632, where he met Sienese politician Ottavio Piccolomini.

Upon his return to the grand duchy in 1641, he resumed the reins of Sienese government. He did not stay long, nevertheless, as the Wars of Castro broke out. Ferdinando II vested in him supreme authority over the grand duchy's military affairs, and thus he commanded the league of the Republic of Venice, the Grand Duchy of Tuscany, the Duchy of Parma and the Duchy of Modena and Reggio against the Barberini Pope, entrusting the government of Siena to his brother Cardinal Leopoldo de' Medici for the duration of his absence.