Einhard. The Life of the Emperor Charles. Chapter 15.
Such are the wars, most skilfully planned and successfully fought, which this most powerful king waged during the forty-seven years of his reign. He so largely increased the Frank kingdom, which was already great and strong when he received it at his father's hands, that more than double its former territory was added to it. The authority of the Franks was formerly confined to that part of Gaul included between the Rhine and the Loire, the Ocean and the Balearic Sea; to that part of Germany which is inhabited by the so-called Eastern Franks, and is bounded by Saxony and the Danube, the Rhine and the Saale ‹ this stream separates the Thuringians from the Sorabians; and to the country of the Alemanni and Bavarians. By the wars above mentioned he first made tributary Aquitania, Gascony, and the whole of the region of the Pyrenees as far as the River Ebro, which rises in the land of the Navarrese, flows through the most fertile districts of Spain, and empties into the Balearic Sea, beneath the walls of the city of Tortosa. He next reduced and made tributary all Italy from Aosta to Lower Calabria, where the boundary line runs between the Beneventans and the Greeks, a territory more than a thousand miles long; then Saxony, which constitutes no small part of Germany, and is reckoned to be twice as wide as the country inhabited by the Franks, while about equal to it in length; in addition, both Pannonias, Dacia beyond the Danube, and Istria, Liburnia, and Dalmatia, except the cities on the coast, which he left to the Greek Emperor for friendship's sake, and because of the treaty that he had made with him. In fine, he vanquished and made tributary all the wild and barbarous tribes dwelling in Germany between the Rhine and the Vistula, the Ocean and the Danube, all of which speak very much the same language, but differ widely from one another in customs and dress. The chief among them are the Welatabians, the Sorabians, the Abodriti, and the Bohemians, and he had to make war upon these; but the rest, by far the larger number, submitted to him of their own accord.