Marquess of Castelnuovo (Italian: Marchese di Castelnuovo) was a title in the Peerage of Italy that was created in the late 17th century for Ferdinand van den Eynde, 1st Marquess of Castelnuovo. The marquessate was purchased by the Flemish magnate Jan van den Eynde, at the time one of the wealthiest men in the city of Naples, for his son Ferdinand. Ferdinand married Olimpia Piccolomini, of the House of Piccolomini, by whom he had three daughters. Thanks to the marriage of his heir apparent Giovanna to Giuliano Colonna, the title was inherited by Giovanna's son, Ferdinando Colonna. The title was held for nine generations by the Colonna, before losing statutory regulation and lawful recognition (together with all other Italian peerage titles) upon the establishment of the Italian Republic, w