The presence of Benedictine monks and nuns in the city of Rijeka and its surroundings has so far only been the subject of historiography's interest to a lesser extent. The Benedictine nuns of St. Roko were present in Rijeka from the middle of the 17th to the middle of the 20th century, when they left for Italy, where they live to this day in the abbey of St. Daniel in Abano. The abbey of St. Jakov is the predecessor of today's City of Opatija, to which it gave its name. While the time of the arrival of the Benedictines in the Middle Ages still remains unknown to us, archival sources confirm that the Ottoman incursions in the first half of the 16th century were the reason for the abandonment of the abbey. The Benedictines of the Olivetan congregation came to Opatija in the years before the First World War, to build a church and a monastery by the beginning of the thirties. The presence of the Benedictines in Opatija ends in the middle of the 20th century, when the monks retire to Tkon. The establishment of the independent Diocese of Rijeka after the First World War is closely related to the person of Isidoro Sain, a Benedictine monk from Novigrad in Istria and abbot of Praglia. The episcopate of Isidoro Sain left an indelible mark on pastoral life and the construction of new diocesan structures in the years marked by Italian fascism.