John VIII was pope from 872 to 882. He was a tenacious pope who, despite difficult political circumstances, fought for the implementation of Roman primacy in different contexts, even by devising courageous and audacious strategies. His political choices were greatly influenced by the Saracen threat to Rome. Hoping to obtain military support against the Saracens from the Byzantines, John VIII was forced to restore diplomatic relations with the patriarchate of Constantinople. Then, he deeply influenced the future of the Carolingian family, choosing three emperors. John VIII’s Pontificate is worthy of consideration owing to the pope’s unbending aspiration to extend Roman jurisdiction over new territories in Central and South-Eastern Europe through the creation of an extensive diplomatic network with the local Slavic rulers.