Meanwhile, the accession to the Byzantine throne of Nikephoros I in 802 confirmed the conflict of legitimacy between the Frankish and Byzantine incarnations of the Roman Empire, known in historiography as the problem of two emperors (in German, "Zweikaiserproblem"). According to Theophanes the Confessor, Charlemagne had attempted to prevent that conflict with a project to marry Irene, but this was not completed. The territorial conflicts were addressed in the following years through a series of negotiations known as the "Pax Nicephori", but the broader conflict with Constantinople about Imperial legitimacy proved extremely durable.