The orignis of Piansano are ancient: some findings of flint arrowheads suggest apermanent Eneolithic settlement. Certain is also the presence of the Etruscans, proven by a consistent concentration of various types of burials.
After the capture of Vulci in the third century A.C. The Romans divided the territory and gave rise to new settlements. These today are only represented by fragments of walls, votive terracottas, ceramics and many Roman coins.
Between the fourth and fifth century P.C. there were many incursions by barbarian tribes, who sacked all the territory of Tuscia. Some remains near the Poggio of Metino suggest that a violent siege took place during the war between the Goths and Byzantines.
The situation already not easy in itself, was aggravated by the descent of the Lombards and the settlement was forgotten for a few centuries.
In the Middle Ages, what once it was a small village finally earned the epithet of Castrum, or of a fortified village. Around 1150 Piansano was in the power of the counts of Vetralla, who recently gave away half of their possessions to the city of Viterbo.
In the middle of the following century the Bisenzios became part of the history of the village, with their intrigues, inheritances, betrayals and murders. The family took possession of the castle until 1338, when it passed to the di Vicos and finally to the Farnese (1385), which finally destroyed the castle.
In later centuries the territory of Piansano was given by the Church to various families, until in 1537 was created the Duchy of Castro by Paul III Farnese. With the destruction of Castro in 1649, the city was again confiscated by the possessions of the Church.
In 1790 the territory of Piansano was granted to Count Alessandro Cardarelli of Rome, until 1808, when the Apostolic Camera sold the estate to the Polish Prince Stanislaus Poniatowski. These in turn sold it to Count Giuseppe Cini of Rome, who kept it until 1897 when it was purchased at auction in Monte dei Paschi di Siena.
In 1909 the Tuscan bank sold it to more people from whom it was later expropriated by the National Fighters Opera, which assigned it to the veterans of the Great War. >/p>