Cosimo III de' Medici (14 August 1642 – 31 October 1723) was Grand Duke of Tuscany from 1670 until his death in 1723, the sixth and penultimate from the House of Medici. He reigned from 1670 to 1723, and was the elder son of Grand Duke Ferdinando II. Cosimo's 53-year-long reign, the longest in Tuscan history, was marked by a series of laws that regulated prostitution and May celebrations. His reign also witnessed Tuscany's deterioration to previously unknown economic lows.
Cosimo III married Marguerite Louise d'Orléans, a cousin of Louis XIV. The marriage was solemnized by proxy in the King's Chapel at the Louvre, on 17 April 1661. It proved to be a very difficult marriage. Marguerite eventually abandoned Tuscany for the Convent of Montmartre. Together, they had three children: Ferdinando in 1663, Anna Maria Luisa, Electress Palatine, in 1667, and Gian Gastone I the last Medicean ruler of Tuscany, in 1671.
