Legio I Germanica, the German legion, was a Roman legion, levied in 48 BC by Julius Caesar to fight for him in the civil war against Pompey. After the Batavian rebellion (70 AD), the remaining men of the Germanica were added to Galba's seventh legion, which became Legio VII Gemina. The emblem of Legio I was a probably a bull, like all the other legions levied by Caesar (except the Legio V Alaudae).

I Germanica took part in Caesar's civil wars and fought the Battle of Pharsalus in 48 BC. After the assassination of Caesar, they were loyal to Augustus. Between 30 and 16 BC, the legion was stationed in Hispania Terraconensis, where they fought in the war against the Cantabrians. Around the turn of the century they were moved to the Rhine frontier to fight in Drusus' campaigns against the Germanic tribes.

The Germanica stayed in Germania Inferior until 69 AD, the year of the four emperors. After emperor Galba's dismissal of the Germanic army help, the legions of the Rhine frontier acclaimed Vitellius as emperor and marched with him for Rome. However, Vespasian, a new Emperor candidate, made his bid for power and defeated Vitellius and his army in Italy.

During the Batavian rebellion of 70 AD, Legio I Germanica was one of the legions (the other was Legio XVI Gallica) that went to help the legions besieged in Xanten. However, things did not go according to plan and the rescuing legions ended up imprisoned themselves. The new emperor Vespasian eventually suppressed the revolt, but the disaster of the four defeated legions was notorious. Legio I Germanica was merged with the surviving men of Galba's VII legion to form a new one, Legio VII Gemina.

See also: List of Roman legions