The occasion of these oaths was the alliance between the two brothers, Ludwig the German and Charles the Bald, against their brother Lothar. Lothar had been defeated at the battle of Fontenay, 841, by his brothers, who then made this league. The oaths are given in this form by Nithard, the historian of the later Carolingians, who was the son of Angilbert and Bertha, the daughter of Karl the Great. The lingua romana and the lingua teudisca are the vulgar languages respectively of the followers of Charles the Bald and Ludwig the German, that is, of the inhabitants of France and of Germany. The appearance of a Latin dialect as the language of the inhabitant of the western kingdom indicates that the Roman elements had after all survived in Gaul and were absorbing the German elements; the formation of two languages mutually exclusive in the two portions of the empire suggests a fairly advanced stage of differentiation between the German and the French parts. But the chief interest of this document is in the field of language study. The lingua romana shows an early stage in the development of French from Latin, while the lingua teudisca is one of the earliest forms of Old High German. The lingua romana shows the process by which the French language grew out of Latin; note that inflectional endings have largely disappeared, and case is shown by the use of prepositions, and that phonetic changes (changes of vowels and consonants) have also taken place. Some of the words are good Latin, others are very nearly modern French, and still others stand midway between Latin and French. Most of the words in the lingua teudisca ean be identified with modern German words. Note that each leader took the oath in the language of the followers of the other, in order that his brother's followers might understand him. So Ludwig the German speaks in the lingua romana and Charles the Bald in the lingua teudisca.

So Ludwig and Charles Came together at Argentaria, which is called Strassburg in the common tongue, and there took the oaths which are given below, Ludwig speaking in the lingua romana and Charles in the lingua teudisca.

Ludwig, being the elder, took the oath first, as follows:
Pro deo amur et pro christian poblo et nostro commun salvament, d'ist di in avant, in quant deus savir et podir me dunat, si salvaraeio cist meon fradre Karlo et in aiudha et in cadhuna cosa, si cum om per dreit son fradre salvar dist, in o quid il mi altresi fazet, et ab Ludher nul plaid numquam prindrai, qui meon vol cist meon fradre Karle in damno sit.

When Ludwig had finished, Charles took the oath in the lingua teudisca:

In godes minna ind in thes christanes folches ind unser bedhero gehaltnissi, fon thesemo dage frammordes, so fram so mir got geuuiczi indi mahd furgibit, so haldih thesan minan bruodher, soso man mit rehtu sinan bruodher scal, in thin thaz er mig so sama duo, indi mit Ludheren in nohheiniu thing ne gegango, the minan uuilon imo ce scadhen uuerdhen.

Literal translation of the lingua romana, the lingua teudisca being the same with the names changed:
" By God's love and by this Christian people and our common salvation, from this day forth, as far as God gives me to know and to have power, I will so aid this my brother Charles in each and every thing as a man ought to aid his brother, in so far as he shall do the same for me; and I will never have any dealings with Lothar that may by my wish injure this my brother Charles."

And this is the oath which the followers of each took in their own tongues:
Lingua romana:
Si Lodhuuigs sagrament, que son fradre Karlo iurat, conservat, et Karlus meos sendra de suo part non los tanit, si io returnar non l'int pois: no io no neuls, cui co returnar int pois, in nulla aiudha contra Lodhuuuig nun li iv er.

Lingua teudisca:

Oba Karl then eid, then or sinemo bruodher Ludhuuuige gesuor, geleistit, indi Ludhuuutg min herro then er imo gesuor forbrihchit, ob ih inan es iruuenden ne mag: noh ih noh thero nohhein, then ih es iruuenden mag, uuidhar Karle imo ce follusti ne uuirdhit.

Literal translation of the lingua romana, the same as the other with names changed:
" If Ludwig keeps the oath which he swore to his brother Charles, and Charles, my lord, on his part does not keep it, if I cannot prevent it, then neither I nor anyone whom I can prevent shall ever defend him against Ludwig."