Cassino, he wrote first a history of Rome and then a history of the Lombards, the main source for the history of the duchy to that time as well. Expansion Under Zotto's successors, the duchy was expanded against the Byzantine Empire. Arechis, himself from the duchy of Friuli, captured Capua and Crotone, and sacked Byzantine Amalfi, but was unable to capture Naples. After his reign, Byzantine holdings in southern Italy were reduced to Naples, Amalfi, Gaeta, Sorrento, Calabria, and the maritime cities of Apulia (Bari, Brindisi, Otranto, etc.). In 662, Duke Grimoald I (duke since 647), went north to aid the King Godepert against his brother, the co-king Perctarit, and instead killed the former, forced the latter into exile, and captured Pavia. As king of the Lombards, he tried to reinstate Arianism over the Catholicism of the late king Aripert I. However, Arianism was disappearing even in the duchy, as was the distinction between the ethnic Lombard population and the Latin- and Greek-speaking one. In 663, the city itself was besieged by the Byzantines during the failed attempt of Constans II, who had disembarked at Taranto, to recover southern Italy. Duke Romuald I defended the city bravely, however, and the Emperor, also fearing the arrival of Romuald's father, King Grimoald, retired to Naples. However, Romuald intercepted part of the Roman army at Forino, between Avellino and Salerno, and destroyed it. A peace between the Duchy and the Eastern Empire was signed in 680. In the following decades, Benevento conquered some territories from the Byzantines, but the main enemy of the duchy was now the northern Lombard kingdom itself. King Liutprand intervened several times to impose a candidate of his own on the ducal throne. His successor, Ratchis, declared the duchies of Spoleto and Benevento foreign countries where it was forbidden to travel without royal permission. Secundum Ticinum In 758, king Desiderius briefly captured Spoleto and Benevento, but with Charlemagne's conquest of the Lombard kingdom in 774, Arechis II tried to claim the royal dignity and make Benevento a secundum Ticinum: a second Pavia (the old Lombard capital). Seeing that this was impractical and would draw Frankish attention to himself, he opted instead for the title of princeps (prince). In 787, he was forced by Charlemagne's siege of Salerno to submit to Frankish suzerainty. At this time, Benevento was acclaimed by a chronicler as a Ticinum geminum—a "twin Pavia". Arechis expanded