John X, the Balkans, and Byzantium. Papal Power and Its Limits in Southeastern Europe at the Beginning of the 10th Century

The pontificate of John X (914–928), in particular, witnessed significant interactions between Rome and Southeastern Europe . The pope negotiated with the Byzantine Empire to organise Rome’s defence against the Saracens (915), was summoned by Patriarch Nicholas Mystikos to endorse the resolution of the Tetragamy controversy (920–922/923), established ties with the nascent Croatian kingdom (925, 928), and made at least two attempts to establish diplomatic relations with the Bulgarians (922/923, 926/927). My paper explores John X’s interactions as a lens through which to better understand how the bishops of Rome exercised their power and influence in Southeastern Europe during this period. The cases of Byzantium and Croatia, in particular, highlight that papal authority was actively sought by local actors, while the scope of Roman intervention was simultaneously constrained by the ambitions and interests of regional powers. John’s interactions further illustrate that, in the early tenth century, the church of Rome remained committed to expanding and consolidating its influence in the Balkans.