 Originating in the Early Middle Ages (the name deriving perhaps from the Latin "sommum", meaning "top"), Sonnino is mentioned for the first time in a Papal bull from 999.It was held first by the De Sompnino, and was acquired by Onorato I Caetani in 1369.The castle was inhabited by the Caetani d'Aragona until they sold it in 1469 to the Colonna, who were later followed by the Antonelli and the Talani families.