Terracina was a frontier town on the border between the Patrimonium Sancti Petri and Sourthern Kingdom, and so were its church and diocese. This reason prompted the popes to take special care of the town and its cathedral – S. Cesareo. In this essay the main aspects of diocesan life in the 12th and 13th century are illustrated. The enlargement of the diocese in the second half of the 11th century is first discussed, together with the union of the dioceses of Sezze and Priverno and the establishment of a vicedominus, coadjutor of the bishop in the diocesan churches. The relationship between bishops and secular clergy is then analysed: Benedectin and then Cistercian religious orders had an important function in managing the pastoral service within churches and monasteries. Florians, Franciscans, and Dominicans were added later, and they had a great impact on local society. Bishops were active in promoting the building of churches and hospitals in peripheral areas and the surrounding countryside, with the aim of increasing population and livability of isolated places; pastoral care was also scrupulously managed: the establishment of a fraterna clericorum and the reception of different laymen as oblates constitute concrete features of the cura animarum. Aiming at the maintenance of common life, bishops also made patrimonial grants to the canons as early as the end of the 12th century, creating two separate mensae – for bishop and canons respectively. Throughout the 12th and early 13th century bishops were elected within the cathedral chapter, but later popes like Boniface VIII intervened on such election.