The name San Valentino is connected to Valentino, bishop of Terracina, who, with his disciple Damiano, on the death of emperor Constantine, began his pilgrimage that led him to Abruzzo. Here he converted and baptized the local people, built new churches and ordained new priests. But a number of pagan priests led the majority of the population against Valentine and his disciple St. Damiano, who were captured, carried to a nearby forest and beheaded. Here they were buried with no worship until the Norman period when, between 1075 and 1078, king Trogisio found the remains of the martyrs, and ordered to bury them in the Oratory located in Castel di Pietra, where countless miracles started to take place. Probably at this time Castel di Pietra changed its name to San Valentino.
Over the centuries it belonged to the Acquaviva family, the Orsini, the de Frigis and to Margherita Farnese of Austria, whose family retained possession until the abolition of feudalism. Since 1863 the words "in Abruzzo Citeriore" were added, to distinguish the place from other comuni of the same name.