On Christmas Day in 800 AD, Pope Leo III crowned Charlemagne as Imperator Romanorum (Latin for "Emperor of the Romans") in Saint Peter's Basilica.
Temporary shift of Venetian loyalties toward the Franks resulted in somewhat permanent naval conflict in the Adriatic, only interrupted by a truce in 807–808.
[1] The result was a joint Frankish and Byzantine expedition to Dalmatia to get the input of the local Romans and Slavs and firmly delimit the borders.
[1] The common belief that the negotiations between Byzantium and the Franks that were held in the early ninth century made Venice an 'independent polity' is only based on the late, allusive and biased witness of Venetian chroniclers such as John the Deacon and Andrea Dandolo and remains therefore highly questionable.
No text of either the treaty, its draft or the preceding negotiations is preserved, apart from a handful of alleged quotations in a mid-century deliberation of Emperor Lothar I in favour of one of the earliest certainly attested Doges of Venice.