High Quality Content by WIKIPEDIA articles! Cosimo III de` Medici (14 August 1642 – 31 October 1723) was the penultimate Medici Grand Duke of Tuscany. 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 ultra-reactionary laws which regulated prostitution and banned May celebrations. His reign also witnessed Tuscany`s deterioration to previously unknown economic lows. He was succeeded by his elder surviving son, Gian Gastone, when he died, in 1723.