Missionary Work in the Balkans
As bishop of Remesiana, Niketas worked among the peoples of Dacia and the surrounding Balkan regions at a time when Christianity was still spreading among the tribes north of the older Roman heartland. The sources connect his preaching particularly with the Bessi, a Thracian people, and present him as one who carried the faith to populations on the frontiers of the Christian world. His contemporaries regarded this missionary labor as the defining achievement of his episcopate.
By one account his activity extended across territories on both sides of the Danube, spanning regions corresponding to modern Serbia, Bulgaria, Romania, Moldova and Ukraine, where he is reported to have founded new communities and ecclesiastical centers; for this work he came to be remembered as an Apostle to the Danube. His contemporary Paulinus of Nola, in praising this mission, called him father of the whole north.
Niketas paired his preaching with the cultivation of liturgical song. He promoted Latin sacred music in worship and is reported to have composed several hymns, treating congregational singing as a means of teaching and confirming converts in the faith. It is in this connection that Saint Jerome and Saint Paulinus of Nola both acknowledged his poetical gifts.