Foundation
There are two theories about I Germanica recruitment. The most favored is that it was raised by Julius Caesar in 48 BC to fight in the civil war against Pompey. In that case it would have fought in the Battle of Pharsalus in 48 BC.
A second theory attributes its recruitment to Gaius Vibius Pansa Caetronianus, a partisan of Caesar, who died in the Battle of Forum Gallorum against Mark Antony in 43 BC. Legio I would have been recruited in that year for that campaign.
However recruited, Legio I was inherited by Augustus and therefore ought to have been entitled to the cognomen Augusta after distinguished service under his eyes; however, there was no Legio I Augusta. One explanation is that an event happened to prevent or take away that name.
Events
48 BC: Possible campaigns with Caesar in the civil war include the battles of Dyrrachium and Pharsulus, but there is no solid complete evidence for this.
46 - 45 BC: Hispania: possible engagements against the holdout armies of Pompeius, including the battle of Munda.
43 - 42 BC: Possibly the Battles of Mutina (43 BC) and Phillippi in Italia (42 BC) with Octavian against Antonius.
38 - 36 BC: Campaigns against Sextus Pompeius, mainly in Sicilia.
25 - 13 BC: Hispania, campaign against the Cantabrians. At some point between the Pompeius and the Cantabrian campaigns it earned the cognoment Augusta but was stripped of it due to disloyal and minor mutinous behavior.
9 - 69 AD: Germania. During its time in Germania it earned the cognoment Germania under either Drusus or Germanicus.
69 AD: Supported Vitellius in his revolt against Galba and was later defeated by Vespanian. The legion was disbanded and never reconstituted at this point.
Distinguished service in Germania
Around the turn of the century, Legio I appears on the Rhine frontier. The Annales of Tacitus state that they received standards from Tiberius, but when that was is not clear. This statement is problematic because only new or reconstituted legions received standards. The legion could have been reconstituted after Spain, but more likely it kept its aquila (which was only taken away on disbandment) and received new vexillae, or manipular standards, which would indicate a reorganization with perhaps replacements.
The legion soon redeemed itself, winning the title Germanica for distinguished service in Germania. Exactly when they won it is not known. They were initially stationed at Oppidum Ubiorum (Cologne) in the jurisdiction that was to become Germania Inferior. For the time being, the province contained five legions and was under Publius Quinctilius Varus.
In AD 9, Varus and three legions were lured away to the north to suffer extinction in the Battle of Teutoburg forest. Fortunately for Legio I he had not taken his entire command but left two legions in camp under legati or junior officers, Legio I being commanded by a nephew of Varus, Lucius Asprenas.
Most likely, the title Germanica was granted for service in Drusus' subsequent punitive and exploratory campaigns against the Germanic tribes. Drusus was extremely popular. It was an honor to be in his service and he made sure that his men were honored properly.
Ranks
Legate
Tribunus Militum
Centurio Primus Pilus
Centurio
Aquilifer
Optio
Tesserarius
Milites
