The Duchy of Castro operated as a functioning State within the Patrimony of Saint Peter. It possessed rich forests full of game, fertile vineyards and fields, and a great number of fortresses. In the consistory of 14 March 1537, the Pope also awarded his son the cities of Nepi and Ronciglione. Pier Luigi was tasked with repairing all the fortresses over which he was now feudal lord. The new Duke commissioned Antonio da Sangallo the Younger to create a new capital, which saw the construction of a citadel, ducal palace and mint.