The city then gave its name to the medieval Slavic kingdom of Dioclea (in Slavic Duklja), later called Zeta, whose rulers are often referred to as "most beloved sons of blessed Peter." The *Annales presbyteri Diocleatis*, the oldest Slavic chronicle in the South, written in Antivari by an anonymous Catholic priest of the 12th century, speaks of Dioclea as a land entirely Catholic, belonging to Red Croatia (*Cracatia Rubea*). Similarly, several Byzantine historians repeatedly refer to the leaders and people of Dioclea as Croats. Even the founder of the Serbian dynasty, Stefan Nemanja, father of St. Sabbas, received Latin Baptism in Ribnica (now Podgorica), because only Latin priests were found there.
At that time, there existed the dioceses of Svacium (Svač), Oleinium (Dulcigno, Ulcinj), and Antibarum (Antivari, Bar), initially suffragans of the metropolitan of Durrës, then of that of Ragusa from 1022, and finally of Split until 1087, when Antivari became a metropolitan see, first temporarily and later, from 1178, permanently, with about ten suffragan sees. In the 13th century, Antivari, thanks to the zeal of some of its bishops, played a leading role in the reconquest of northern and central Albania for Catholicism. It did not, however, achieve equal success in defending Catholic positions in the territory of Duklja, since this was incorporated into Serbia around 1180. Soon after, this land felt the invasion of the Serbian national Church, an invasion facilitated, it seems, by the existence of various rites and liturgical languages among the local Catholics (monasteries of Latins, Greeks, and Slavs). Sabbas Nemanja, the Serbian national saint, immediately after the establishment of the autocephalous Serbian Church in 1219, established some Eastern episcopal sees even in the Catholic provinces of Zeta and Chlemo-Hum (today Herzegovina). Later, particularly under King Uroš II Milutin, open persecutions of Catholics ensued. With the disintegration of the Serbian Kingdom after the death of King Stefan Dušan (1331–55), the Catholic Church
did not succeed in maintaining its position, despite the regional councils held in the Moraca monastery in 1648 and 1653.
The legal status of the Church was definitively regulated by the Concordat between the Holy See and the Kingdom of Montenegro (1886).