The name came into use after Julius

The name came into use after Julius Caesar and whether it was used widely before him amongst Romans is unknown. The term may be Gallic in origin. Caesar reports hearing from his Remi allies that the term Germani was used for the group the Romans called the Germani Cisrhenani, and that these tribes had historically come from over the Rhine. So the name Germania seems to have been extended to cover the similar tribes in the area understood to be their homeland.[5][6] Some generations later, Tacitus claimed that this is precisely what happened, saying that the Tungri of his time, who lived in the area which had been home to the Germani Cisrhenani, had changed their name, but had once been the original Germani. Tacitus wrote in AD 98:

For the rest, they affirm Germania to be a recent word, lately bestowed. For those who first passed the Rhine and expulsed the Gauls, and are now named Tungrians, were then called Germani. And thus by degrees the name of a tribe prevailed, not that of the nation; so that by an appellation at first occasioned by fear and conquest, they afterwards chose to be distinguished, and assuming a name lately invented were universally called Germani.[7]

The Germania of Caesar and Tacitus was not defined along linguistic lines as is the case with the modern term "Germanic". They knew of Celtic tribes living in Magna Germania (Greater Germania), and what we now term Germanic tribes living in Gaul, then a predominantly Celtic region. It is also not clear that they distinguished the tribes into linguistic categories in any exact way. The language of the Germani Cisrhenani and their neighbours across the Rhine is still unclear. Their tribal names and personal names are generally considered Celtic, and there are also signs of an older Belgic language which once existed between the contact zone of the Germanic and Celtic languages.

Germania in its eastern parts was likely also inhabited by early Baltic and, centuries later, Slavic tribes. These parts of eastern Germania are sometimes called Germania Slavica in modern historiography.