The primary sources for Frankish military custom and armament are Ammianus Marcellinus, Agathias, and Procopius, the latter two Eastern Roman historians writing about Frankish intervention in the Gothic War. Writing of 539, Procopius says:

In 447 Attila again rode south into the Eastern Roman Empire through Moesia. The Roman army under the Gothic magister militum Arnegisclus met him in the Battle of the Utus and was defeated, though not without inflicting heavy losses. The Huns were left unopposed and rampaged through the Balkans as far as Thermopylae. Constantinople itself was saved by the intervention of the prefect Flavius Constantinus who organized the reconstruction of the walls that had been previously damaged by earthquakes, and, in some places, to construct a new line of fortification in front of the old. An account of this invasion survives:

The language spoken by the early Franks is known as Old Frankish and is only attested in a few words in the Lex Salica and in personal names, and is mostly reconstructed from Old Low Franconian and loanwords in Old French and Latin. In the Low Countries it evolved into Old Dutch. Though it lent its name to a number of widely spoken dialects in modern Germany (Ripuarian, Moselle-Franconian, Rhine-Franconian, East-Franconian, South-Franconian), France (Lorrainian) and Luxemburg (Luxembourgish) these languages are not directly related to the ancient language of the Franks.[10] Early in their history the Salians adopted Latin as a second language, as in the case of the Ubii. South of the language border, in what became northern France (langues d'oïl), Frankish was replaced by Old French from the 8th century on. Thereafter the language border between the French and Dutch languages slowly moved north to its current location. There is no surviving work of literature in the Frankish language and perhaps no such works ever existed. Latin was the written language of Gaul before and during the Frankish period. Of the Gallic works which survive, there are a few chronicles, many hagiographies and saints' lives, and a small corpus of poems. The word Frank has the meaning of "free" (e.g. English frank, frankly, franklin, or the Dutch expression "Frank en Vrij": Frank and Free). This arose because, after the conquest of Gaul, only Franks were free of taxation.[11]