What wasn't a boundary for the empire of Charlemagne?

The empire of Charlemagne, known as the Carolingian Empire, did not have fixed geographical boundaries that remained constant. Its territory fluctuated due to military campaigns and political alliances, encompassing large parts of Western and Central Europe, including modern-day France, Germany, the Low Countries, Switzerland, and parts of Italy and Austria. Additionally, Charlemagne's influence extended beyond these territories through cultural and ecclesiastical ties, promoting the spread of Christianity and Latin culture, which further blurred the lines of his empire's boundaries.