Mattias de' Medici
Portrait byJustus Sustermans,c. 1660
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
House	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 ofGrand Duke Cosimo II de' Medici of Tuscany andArchduchess Maria Maddalena of Austria. He was governor of Siena, with interruptions, from 1629. He never married.^[1]

Mattias pursued an ecclesiastical career, like his brotherGian 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 byFerdinando 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,Caterina de' Medici.^[2]

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.^[2] In 1631, he joined the Austrian belligerency in theThirty Years' War. He took part in the famousbattle of Lützen,^[3] in November 1632, where he met Sienese GeneralOttavio Piccolomini.

Upon his return to the grand duchy in 1641, he resumed the reins of Sienese government. He did not stay long, nevertheless, as theWars of Castro broke out. Ferdinando II vested in him supreme authority over the grand duchy's military affairs,^[2] and thus he commanded the league of theRepublic of Venice, theGrand Duchy of Tuscany, theDuchy of Parma and theDuchy of Modena and Reggio against theBarberini Pope, entrusting the government of Siena to his brother CardinalLeopoldo de' Medici for the duration of his absence.^{[citation needed]}

Mattias adored the arts, patronisingJustus Sustermans,Volterrano and many other eminent artists. He also loved horse races and was particularly enthusiast of the famousPalio, which he promoted during its early history. While in Germany, he acquired scientific instruments, such as dials, astrolabes and compasses; all of which he later deposited in theUffizi.^{[citation needed]}

In later life, suffering from gout, he pondered re-assuming ecclesiastical garb; however, he fell ill and died in Siena on 11 October 1667 at 54 years of age. He was buried in the Medici tombs inSan Lorenzo, Florence.^[4]

• Young, G.F.:The Medici: Volume II, John Murray, London, 1920

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