What is Cosimo III de' Medici, Grand Duke of Tuscany?
{{Infobox royalty | type = monarch | name = Cosimo III | image = Volterrano, Cosimo III de' Medici in grand ducal robes (Warsaw Royal Castle).jpg | caption = Cosimo in granducal robes, with Tuscan regalia | reign = 23 May 1670 – 31 October 1723 | coronation = | succession = [[Grand Duke of Tuscany]] | predecessor = Ferdinando II | successor = [[Gian Gastone de' Medici, Grand Duke of Tuscany|Gian Giastone]] | spouse = [[Marguerite Louise d'Orléans]] | issue = [[Ferdinando de' Medici, Grand Prince of Tuscany|Ferdinando, Grand Prince of Tuscany]]<br/>[[Anna Maria Luisa de' Medici|Anna Maria Luisa, Electress Palatine]]<br/>[[Gian Gastone de' Medici, Grand Duke of Tuscany|Gian Gastone, Grand Duke of Tuscany]] | issue-link = #Issue | full name = Cosimo de' Medici | house = [[House of Medici]] | father = Ferdinando II de' Medici | mother = [[Vittoria della Rovere]] | birth_date = 14 August 1642 | birth_place = [[Pitti Palace]], [[Florence]], [[Grand Duchy of Tuscany|Tuscany]] | death_date = {{death date and age|df=yes|1723|10|31|1642|08|14}} | religion = [[Roman Catholicism]] | death_place = Pitti Palace, Florence, Tuscany | burial_place = Basilica of San Lorenzo, Tuscany }} '''Cosimo III de' Medici''' (14 August 1642 – 31 October 1723) was the penultimate [[Grand Duke of Tuscany]]. He reigned from 1670 to 1723, and was the elder son of [[Grand Duke Ferdinando II of Tuscany]]. Cosimo's fifty long reign, the longest in Tuscan history, was marked by a series of regulatory laws. His reign also saw Tuscany's bad finances become even worse. He was succeeded by his elder surviving son, [[Gian Gastone de' Medici]], when he died, in 1723. He married [[Marguerite Louise d'Orléans]], a cousin of [[Louis XIV]]. It was a bad marriage and Marguerite Louise eventually left Tuscany to remain at the Conve