The Celtic God Teutates was equated by the Romans with their own Mars, a war deity and Mars in turn was associated with the Germanic *Tiwaz. My article The Celtic God Teutates published on this blog on 25/1/09 goes into more detail about this deity. What I would like to do here is develop this link further.
As Jaan Puhvel establishes in his Comparative Mythology "Teutates (Toutates, Totates, Tutates) is derived from Proto-Indo-European *tewta" and this means 'people'. The Old Irish tuatha and the Gothic thiuda are derived from this so this means that the deity was originally common to both the Celtic and Teutonic peoples, reaching back into a shared past but after Proto-Indo-European times. It is in other words an ancient concept. Both the Teutons and the Celts had a tendency to name themselves after various Gods who were considered to be the fathers and founders of their tribes.
In my article Tuisto, the God *Tiwaz published on 7/4/14 I explored the connection between the ancient deity referred to in Tacitus' Germania, Tuisto and *Tiwaz.
"If the earthborn Tuisco, the ancestral god of our nation, stands (as Zeuss p.72 has acutely suggested) for Tivisco, Tiusco, it shews on its very face the meaning of a divine heavenly being, leaving it an open question whether we will choose to understand it of Wuotan or any other god, barring always Tius himself, from whom it is derived." (Teutonic Mythology Volume 1, Jacob Grimm)
The Teutonic peoples never referred to themselves as 'German' or 'Germanic'. This is an alien term conferred on them by the Romans. Instead they referred to themselves either by their tribal names or sometimes collectively as Teutons. This name was originally the possession of one particular tribe called the Teutones or Teutoni, Latin for 'Teutons'. In 105BCE Teutobad, the King of the Teutones achieved victory over the Romans in the Battle of Aurosio.
The terms Dutch and Deutsch are derived from the Proto-Germanic *Þeudiskaz (meaning 'of the people', ie 'folk'), the root of Dutch, Deutsch and Teuton. This is also the meaning of Old English þeod, the Lithuanian tauta and the Old Irish tuath. In turn *Þeudiskaz is derived from the Proto-Indo-European *teuta ('people'). The children of Tuisto derived their collective name from Him:
"In ancient lays, their only type of historical tradition, they celebrate Tuisto, a god brought forth from the earth. They attribute to him a son, Mannus, the source and founder of their people, and to Mannus three sons, from whose names those nearest the Ocean are called Ingvaeones, those in the middle Herminones, and the rest Istvaeones. Some people, inasmuch as antiquity gives free reign to speculation, maintain that there were more sons born from the god and hence more tribal designations- Marsi, Gambrivii, Suebi, and Vandilii- and that those names are genuine and ancient."(Germania 2.2, Tacitus, J.B. Rives translation)
"In the traditional songs which form their only record of the past the Germans celebrate an earth-born god called Tuisto. His son Mannus is supposed to be the fountain-head of their race and himself to have begotten three sons who gave their names to three groups of tribes- the Ingaevones, nearest the sea; the Herminones, in the interior; and the Istaevones, who comprise all the rest. Some authorities, with the freedom of conjecture permitted by remote antiquity, assert that Tuisto had numerous descendants and mention more tribal groups such as Marsi, Gambrivii, Suebi, and Vandilii-names which affirm to be both genuine and ancient." (H. Mattingley translation, revised by S.A. Handford.)
There is also a conceptual link between Teuton (people/folk) and Arya. In Old Irish Arya is Airya and means 'free man'. In Germanic society one was not a man unless he was free, free to carry weapons and vote in the All Thing that is. The term 'Aryan' has been reconstructed by Professor J. P. Mallory from the Proto-Indo-European (PIE) root heryos meaning "member of one's own group". Mallory (2006) further adds that:
"The evidence suggests that the word was, at least, initially, one that denoted one who belongs to the community in contrast to an outsider". (J.B. Mallory and D.Q. Adams in The Oxford Introduction To Proto-Indo-European and the Proto-Indo-European World)
This is further evidence for the antiquity of *Tiwaz and His ancient racial relationship with the Germanic and closely related northern Indo-European peoples.