842: The Oaths of Strasbourg

In 842, Charles the Bald and Louis (called “the German”) seal their alliance against their brother Lothair. The Oaths of Strasbourg are a military and political episode, but also a famous moment in the history of languages.

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⚔️ An alliance against Lothair

After Louis the Pious’s death (840), war breaks out among heirs. Charles and Louis seek to secure a durable coalition. The oaths are pronounced before their troops to make the commitment public and credible.

In 841, the alliance has already proved decisive on the battlefield: Charles and Louis win at Fontenoy‑en‑Puisaye, weakening Lothair. The crisis is also fed by other claims, especially in Aquitaine, where Pepin II contests Charles’s authority.

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🗣️ Two languages, one goal

The episode is famous because the oaths are formulated so that each army can understand:

• one oath is spoken in a “Romance” language (close to vernaculars derived from Latin),
• the other in a “Teutish” (Germanic) language.

This choice does not “invent” French, but it shows that the empire’s linguistic unity is already broken: governing requires taking real spoken languages into account.

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🧠 Key takeaways

• The oaths are a military alliance act in the Carolingian civil war.
• They reveal a durable linguistic divide between Romance West and Germanic East.
• They foreshadow the political partition stabilised at Verdun (843).