The name of the town should derive from Pozzo Gallo as depicted in the municipal coat of arms.
According to tradition, Pozzaglia was founded by Charlemagne’s troops after defeating the Saracens in the ninth century and it became a possession of the Abbey of Farfa. In the thirteenth century it was given to Cardinal Pietro Colonna, excommunicated in 1297 for denying the legitimacy of Pope Boniface VIII (with reference to the slap of Anagni). The successor, Benedict XI dissolved the excommunication in 1306 and Clement V returned the land to the Colonna.
In 1360 it was attacked and destroyed by the papal militia, and in 1401 passed to the Orsini, then to Muti and Borghese in 1632.
Pozzaglia until 1911, is a derivative of “pozzo”, a frequent epithet in Lazio to indicate a boggy place, an artificial excavation or karst pits, often associated with water sources.