The Caserma Guelfa is a building located along State Road 16 near the intersection with Via del Mare. It is a fortified building with a quadrangular plan dating back to the 16th century, with corner 'strut' bodies and an internal cloister, and a stone entrance portal with a coat of arms of the city of Ascoli. Initially used as the Port Hospice, Hostaria and new warehouses for storing goods, it later took on the role of the last papal outpost before the Kingdom of the Two Sicilies. This is why it is popularly referred to as the "Pontifical Customs House".