The settlement was a small, poor and largely abandoned village at the time of the founding of the Duchy of Castro (1537) before becoming the capital. The Farnese decided to transform it to make it worthy of the rank of capital of the duchy and a symbol of their power and prestige. The reconstruction embraced the city in all its aspects, from defensive walls to public buildings, from noble palaces to houses and streets, turning the settlement into a perfect example of Renaissance art and architecture. Powerful families, Pope Paul III. Farnese as well as many nobles who competed in building noble palaces and made Castro a fashionable city. The heart was represented by Piazza Maggiore, in the center of which there was a fountain and along its perimeter the Palazzo della Zecca, the Hostaria, to welcome the Duke's illustrious guests, the residence of these and the palaces of the most important citizens. Castro also had brick streets and squares with sewers, which was very rare at the time. Sangallo's drawings remain in Florence as proof of this. In Castro there were 13 churches, the most important of which was certainly the Romanesque cathedral dedicated to San Savino, protector of the city, celebrated on May 3 in the main square with a carousel and a palace between the districts. There was also a hospital and hospice to help widows and orphans. To solve the problem of water shortages, a fountain called Santa Lucia was built, located near the church of the same name, with spiral staircases similar to those of San Patrizio in Orvieto.
In 1649 the papal troops of Innocenzo X Pamphilj, whose family was an ally of the Barberinis and an enemy of the Farnese, besieged the city, sacked it, razed it to the ground and deported its inhabitants. Today the ruins are covered with forest. Over time, excavations have been carried out that have brought to light the remains of the main square with its pavement, the remains of the Cathedral, those of the Palazzo della Zecca, the Convent of San Francesco, the fortifications and Porta Lamberta. One can also see the remains of underground rooms, cellars, wells, cisterns and cellars