The diplomatic protocol observed by the Visigothic kingdom of Toledo still lacks a deep study, despite having at our disposition an important epistolary collection, the Epistulae Wisigothicae. The present study focuses on some letters from this collection: those exchanged between King Sisebut and the Byzantine patricius Caesarius. During an open conflict between emperor Heraclius and King Sisebut (c. 614-615), some embassies were sent by both parties to conclude a peace treaty, from which these letters emerge. Through the analysis of their contents, some common features of diplomatic protocol, some shared practises, and perspective differences between both states can be defined.