Oath of Strasbourg

In 842, Louis the German, son of Louis the Pious, and ruler of the eastern Frankish kingdom, met with his brother, Charles the Bald, ruler of the western Frankish kingdom, at Strasbourg. At this meeting, Louis and Charles pledged their allegiance to each other - and their opposition to the Emperor, their elder brother Lothar.

According to our chief source for the meeting, Nithard's Life of Louis the Pious, each king swore the oath in the vernacular of the other's kingdom. Historians have long used this passage to illustrate the theory that, by 842, Carolingian society had begun to split into separate proto-countries with different languages and customs. Philologists are more interested in the texts of the oaths themselves; in a version of Old French, they are one of the first texts we have written in a Romance language clearly distinct from Latin.

In recent years, however, another theory has come to the fore: the Frankish Kingdom comprised several regna (loosely translated as kingdoms) that had always maintained different customs and dialects. In support of this theory is the fact that both Charlemagne and Louis the Pious sent their sons to be raised in the regna they were meant to inherit as their primary territory, in order to guarantee the support of the people by being familiar with them and their customs.