It seems that popular culture likes to draw similarities between Celtic and Germanic peoples. They’re often thought of as “Northern barbarians” who loved fighting naked, painting or tattooing their bodies, making art with knots and spirals, and worshipping either violent gods, or peaceful nature gods, who enjoyed when their worshippers partied with a lot of booze and/or blood. Sometimes, people talk of Northern Europeans in a way that vaguely either refers to Germanic peoples or Celtic peoples; it gets hard to tell. But there is a certain romanticization of trying to see similarities between them.
Today, Germanic and Celtic are linguistic terms first: these people are defined as belonging to either category because Germanic or Celtic languages are or have been spoken by speakers from specific population groups. The language here is purposely vague as it is, indeed, a vague terminology, ethnologically.
Archaeologically, we can draw relations between the La Tène culture and Ancient Celts, and the Jastorf culture with the Ancient Germans. But the lines are blurry and one particularly spicy question we can ask is, if today’s Germany used to be mostly Celtic, when did it become German? When do we see Germanic peoples first coming in and making up most of the population? When is the fait germanique a thing?
That question is not a topic I want to address here, but it relates to this bigger question: Gaulish, Celtic, Germanic, what do these words mean?
The Celts have had many names given to them in the past millennia. The first one here, Celt, doesn’t have a very clear etymology. It comes to us first from Greek writers, who speak of Keltoi living in the Keltikê, which was not the later region called Celtica by Caesar, but the whole Continental Celtic/Gaulish world, literally “where the Celts live” for the Greeks. Interestingly, the Greeks might not have seen the Brittonic peoples as “Celts”. Strabo, quoting Pytheas, talks of a people he identifies as Britons, that Pytheas has misidentified as Celts. Similarly, Strabo also described the customs of the Britons as similar to the Celts and I think this points to Strabo understanding the Celts and Britons as two different groups; why would Strabo need to point out their similarities if the reader knows that the Britons are Celts? It is also worth mentioning for this last point that it makes sense the Greeks would not have called the Britons “Celts”, as for them the Keltikê was essentially the Continental Celtic world. The Greeks also didn’t have our modern notion of comparative linguistics which would have understood the linguistic similarities as being relevant to identifying either group as coming from the same source. Coming back to Caesar, the reason he calls a specific region of Gaul (or one of the three Gauls) Celtica is because, according to him (and freely translated by me here): “for in their language are called themselves (the) Celts”
An etymology for the word Keltos might come from a root meaning “to cover, to hide”, which some writers also see in the deity’s name Sucellos, but the etymology of “good striker” seems correct enough considering the hammer Sucellos wields.
Speaking of etymology, there’s another root that’s a bit more certain and was also more productive, giving us two words: the root gal-, meaning “being able” or “being strong”. This is most likely the root being the words “Gallic” (gallicus and Gallus in Latin) and “Galatian” (but not Gaulish which we will come to soon enough). That is the root behind our group’s name, Touta Galation, where the -ion is a plural genitive ending, so meaning “Tribe of the Gauls” from a reconstructed nominative root *Galatis. This last root is seen in the Ancient Greek word for the Gauls, “Galatês”, which then gave us the English word “Galatian” which now refers specifically to the Celtic population who migrated, following Brennos’ campaigns, to Anatolia (today’s Turkey). You will see the Greek word often translated as “Galatian” in English, which I find incredibly misleading, since it surely refers to the Gaulish population in general and not just those who lived in Anatolia.In the Latin world, Gallus is the noun that means “Gaul” and Gallia the noun that means “Gaul” as in, the region(s), and gallicus, the adjective translated in English as either “Gaulish” or “Gallic”, all Latin worlds that can be related to the same gal- root and the reconstructed *Galatis word.
It could also be possible that this gal- root is behind the word “Celt”, but that would require a mutation or phonetic “confusion” of some sort between g and k, and a and e. Confusion does not mean the people who mixed up g and k did so because they “didn’t know”, or they were “confused” in the first meaning of the word, but that the sounds could vary depending on certain contexts, or the confusion could well have just happened in the writing, or it could have really been confused by a non-native speaker then written down.
Now, Gaulish and Gaul, in English, are what we call in linguistics “false friends”, since while they look like the words Gallic, Gallus or Galatis, they do not come from the same root! It is a coincidence that they look similar. In fact, in comes from a Germanic root *walha meaning “foreigner” which also gave us the words Welsh, Wales, and the -wall in Cornwall.  The Franks met with a Gallo-Romance population and gave them a name from the root *walha. Words that start with w- in Frankish regularly mutate to start with g- afterwards in French. So “Gaul” in English comes from French “Gaule”, and then each language came up with the words “Gaulish” and “gaulois”, while Old English speakers called the Cumbric populations similarly, but Old English word initial w- didn’t mutate, so now we have the words “Wales” and “Welsh”.
Now we get to the word “Germanic”! Over my years of studies, I’ve noticed a confusion with the term “German” as it can refer to many things: the population of Germany, speakers of the German language (Hochdeutsch, opposed to “German languages” that don’t have stately prestige), speakers of German languages (Hochdeutsch, Alemannic or Plattdeutsch, and others I might be unfortunately not aware of or forgetting about) and, finally, people who spoke Germanic languages during the Roman era.
Thus, in Classics and Ancient History, the word “Germans” is synonymous with “Germanic peoples” and sometimes even called “Germanics”, in an attempt to depart from the confusion with the modern conception of “German” from Germany. In a very broad definition, Germanic peoples of the Iron and Roman Ages originated from today’s Denmark and spread to other parts of Scandinavia and Continental Europe. Their spread southwards in today’s Germany is well known, but they also moved to more Easternly places such as the Pontic Steppe or today’s Ukraine. By the time of Julius Caesar, the Germanic peoples are coming into Gaul from all the way across the Rhine, from North to South which could imply that they settled down in these regions, but Caesar also mentions the celticity of either side of the Rhine. It is not a very simple topic, and the information will always be blurry, since there could have been a Germanic migration into the upper Rhine regions with limited numbers, but who could have had a significant impact on Gaul. Of course, we have to say here, that these people, at least, before their Christianization and their learning of Latin, did not call themselves German or Germanic. The word is an exonym. This did not mean that the fait germanique like scholars intent didn’t exist, culturally and linguistically, however.
Still speaking of Caesar, the first mention of the word “German” (or germanus in Latin) that I could find is indeed in Caesar’s Gallic Wars. Indeed, there are also the Cumbri and the Teutones who fought with Rome half a century earlier, but they weren’t called Germans. The Germans of Caesar are characterized by having no druids, living simply, being quite warlike but honorable and, first and foremost, menacing the peace in Gaul. Caesar’s war starts with him intervening in local wars, and one of them was caused by Ariovistus’ expedition into Gaul. Caesar justifies his war by saying first that Gaul needs to be pacified since the Gauls are a menace to Rome (referencing the other Brennos’ sack of Rome centuries earlier) and secondly because the Germans are a threat to Gaul and this peace. In his work, Caesar mentions time and time again Germanic tribes crossing the Rhine into Gaul, becoming a threat, and then when they stop being a threat, they fall back behind the Rhine. We could conclude here that Caesar’s Gaul end at the Rhine, like many authors thought at the time, and his Germany starts with the Rhine, while also understanding that this did not represent the geographical reality.
Still speaking of the word germanus, one quote that I like to analyze to understand its etymology and ancient usage, is one by Strabo:
“Thus it seems to me that the Romans gave them(the Germans) the name because they wished to consider them genuine Galatians, as “germani” means “genuine” in the Roman language.” –Geographica, 7.1.2
This etymology, or meaning, as “genuine” in Latin is not something that I could find. In fact, the etymology behind germanus is still unclear. More strikingly, the word doesn’t look like any Latin word that means “genuine” so I don’t know what Strabo is talking about here. And, most strikingly, he says the Germans are Gaulish! So, is the Germanic/Celtic divide that I just spent minutes describing to you false, or maybe misleading? The way I can understand this confusion here is that the Romans, as shown by Tacitus in his Germania, thought the Germanics to be the “perfect barbarians”. In a way, one could say they needed to explain why they never conquered them. By saying that they were too barbaric, too “strong”, too “genuine” even maybe, they justified that they left them alone. Ancient authors probably didn’t care as much as we did about categorizing these peoples accordingly, instead judging them according to other contexts and here, Caesar, and Strabo are speaking from a general point of view of justifying Roman conquests and elevating Roman might.
Finally, about this quote, Strabo tells us it’s the Romans who gave them their names. This corroborates the fact that it was an exonym, and it could point towards the idea that Caesar came up, not with the word, but the usage of the word. Tacitus however speaks of Germanus being an endonym, a word coming from the Germanic peoples themselves. He explains that it was a tribe called themselves the Germani who migrated into Gaul, who then the locals called “Tungrians”.
The fact of the matter is, with these terms, Gaulish, Gallic, Celtic, Germanic, depending on the context of the usage, they can be more or less appropriate. When reading an ancient author, be careful about the translation by looking up what word was used in the original writing and by looking at the historical context behind the text. When reading an author who writes between that era and us, be sure to understand, again, the context. Finally, when we, today, use these ethnographical terms, we are much more aware of the subtle nuances than historical authors were. We have linguistics, archaeology and historiography behind their usage, and I doubt somebody someday, will claim, academically, that the Dutch are actually Celtic. While the linguistic categorization between Celtic and Germanic is very clear, it can be blurrier in history and archaeology, but we do have ways to at least make an educated guess and associate different archaeological cultures with different peoples and different languages. It is more about probabilities and what is more likely. There is thus a general understanding of what these terms mean that is more or less correct nowadays. It’s more the ideas that the words bring up that we have to be careful about.
Delamarre, Xavier. 2018. Dictionnaire de la langue gauloise. Paris: Errances.
Harland, Philipp A. ‘Celts / Gauls: Cicero and the link between imperial conquest and negative stereotypes (mid-first century BCE),’ Ethnic Relations and Migration in the Ancient World, last modified March 3, 2023, http://philipharland.com/Blog/?p=10065
Matasović, Ranko, and E.J. Brill. 2009. Etymological Dictionary of Proto-Celtic. Brill.
Miller, Katherine L. 2014. The Semantic Field of Slavery in Old English: Wealh, Esne, Þræl. University of Leeds.
Murdoch, Brian O., and Malcolm Read. 2004. Early Germanic Literature and Culture. Rochester, NY: Camden House.
Scott, Lionel. 2021. Pytheas of Massalia: Texts, Translation, and Commentary (1st ed.). Routledge.
Tolkien, J.R.R. 2006. Les monstres et les critiques et autres essais. Paris : C. Bourgois.
Gulick, C.B. trad. (1941) Athenaeus: Deipnosophistae. Loeb Classical Library. Harvard University Press.
Nisard, M. trad. (1865) Jules César: De Bello Gallico. Bibliotheca Classica Selecta.
 A 2015 study showed that people living in today’s Ireland, Wales and Scotland are way more diverse genetically than those living in England. https://www.bbc.com/news/science-environment-31905764
 La Tène is an archaeological site in Switzerland associated with the Celts, and there is a general idea that Celtic culture spread from the Alps to the rest of Central and Western Europe. See map following the main text.
 Κελτῐκή in Classical Attic Greek
 (Geographica, 2.1.18), cited from (Scott 2021) who also understands the same conclusion at p.116. Here Pytheas didn’t claim the Britons were Celts, but that the people mentioned were Celts and not Britons.
 (Geographica, 4.5.2), idem
 « tertiam, quī ipsōrum linguā Celtæ » Interestingly, the noun is “celta”, a first declension but of masculine gender, like the noun “nauta”.
 (Matasović and Brill 2009, p.199) for the etymoogy of Sucellos, see (Delamarre p.113)
 (idem, p.150)
 Γαλάτης in Classical Attic Greek
 Geographica, 8.6.3, and more references on this entry of the Bailly etymological dictionary free of access here https://outils.biblissima.fr/fr/eulexis-web/?lemma=&dict=LSJ
 Like in English, the sound /e/ can be reduced to a sound close to “uh”, without necessarily being noticed or (mis)understood by the speaker. I’d use the example of “rebel” as the noun and “rebel” as the verb. We could see these words written phonetically as “rebul” or “rubel”, as the letter u can be used to represent that “uh” sound (like I just did with “uh”), thus we would say there is a confusion between e and u in the writing. On non-native confusion, we can quote Athenaeus talking about corma (Deipnosophistae, IV, 22) when Delamarre gives the word as curmi, denoting non-native confusions of o/u and a/i.
On the topic of linguistic confusion, we also have historical examples as with Latin Cnaeus/Gnaeus and the word gladius which comes from an uncertain Celtic language, but we know that it would be cladion in Gaulish.
 (Tolkien 2006, 136)
 (Miller 2014)
 Interesting fun fact, the French word “gaillard” meaning something like “good fellow” as a noun or “bawdy” as an adjective, comes from that gal- root according to the Centre national de ressources textuelles et lexicales https://www.cnrtl.fr/etymologie/gaillard It could be a possible French reconstitution for the ethnonym!
 (Murdoch & Read 2004) for a source about these Germanic matters. About the Eastern migration, the Goths are classified as “Eastern Germanics” speaking a East Germanic language. They might have originated from a place near the Baltic Sea, which would place them East of the other Germanics from Jutland and Germany.
 De Bello Gallico, 6.2, here Caesar speaks of the Celts on either side of the Rhine. As for the presence of Germanics in the lower Rhine Caesar mentions it in numerous places, as for the Upper Rhine region one thing of note is Ariovistus and his Germans fighting in today’s Alsace.
 And it is uncertain if they were Germanic or not. The Teutones’ name could well come from Gaulish “teuta”. On this matter, we can notice Ariovistus’ name which is Gaulish, not Germanic (“ario-“ noble, “vistu-“ knowledge, Delamarre 2018)
 Interestingly, even Cicero supported this cause (Harland 2023)
 To corroborate on Gaul ending at the Rhine, Pliny’s Natural History 4.17, and Strabo’s Geographica, , 1.4.3–4, 4.1.1, and 7.1.2. As for the territory of the Germans, Caesar himself in De Bello Gallico in several places, as mentioned, but also Tacitus in Germania, in the first sentence of the text.
 The translation says “Galatian” but we saw that this actually means “Gaulish”.
 “The name Germany, on the other hand, they say, is modern and newly introduced, from the fact that the tribes which first crossed the Rhine and drove out the Gauls, and are now called Tungrians, were then called Germans. Thus, what was the name of a tribe, and not of a race, gradually prevailed, till all called themselves by this self-invented name of Germans, which the conquerors had first employed to inspire terror.”
 The Middle Ages can be complicated as to how they categorize peoples, especially in Medieval Latin. I do not have a source for this, just a general feeling :). As for Post-Medieval writings, be on the lookout for racism and colonial ideas.