Information on Leg. XIII  Gemina

Legio XIII Gemina 

Julius Caesar
(Musei Vaticani, Roma) Legio XIII Gemina: one of the Roman legions.  Its name means 'the twin legion'.
The thirteenth legion was recruited by the Roman general Julius Caesar in 57 BCE, during the war in Gaul, before he attacked the Belgians. He implies the existence of a this unit in his account of the battle against the Nervians, describes how it encountered the Aremoricans and states that it was present during the siege of Gergovia. The blockade of Alesia in 52 must have been among this unit's first operations as well.

During the civil war against Caesar's fellow-triumvir and rival Pompey the Great the men of the thirteenth legion were with Caesar when he crossed the Rubico in January 49. (Caesar, Civil War, 1.7-8; The Thirteenth was the legion with which, as the historian Livy said, Caesar assailed the world.)

the Rubico bridge today
After the conquest of Italy, the legionaries stayed in Apulia for some time. In the winter of 49/48, however, they served at Dyrrhachium. After the decisive battle at Pharsalus, the soldiers were sent back to Italy to be pensioned off (Autumn 48), but in 46, they participated in Caesar's African campaign. They were probably also present during the battle of Munda (45). When Caesar's sole rule was safely established, the legion was disbanded and its veterans were given land at Spello in Italy. 
A new thirteenth legion is mentioned after 41. This was probably not a new creation but a reconstitution of the old unit. However this may be, it was used by Julius Caesar's heir Octavian, who had to put an end to Sextus Pompeius' occupation of Sicily, which put the grain supply of Rome into peril. On one occasion, soldiers of the Thirteenth saved Octavian's life.
When Pompeius was defeated, Octavian and his fellow-triumvir Mark Antony started a war, which culminated in the naval battle off Actium (31), where Octavian defeated his opponent and won the supremacy in the Mediterranean world. From now on, he was known as the emperor Augustus.

The Thirteenth, which was reinforced with soldiers from disbanded legions and was henceforth known as 'the twin legion', was sent to Illyricum or Gallia Transpadana. In c.15, the legion was redeployed in Slovenia, where Augustus' son-in-law Tiberius conquered the Alpine regions. It was now staying at Ljubljana in Pannonia, but the presence of soldiers at Nijmegen in far-away Germania Inferior can be deduced from graffiti.

Tombstone of Publius Urvinus 
(Landesmuseum, Mainz)
In 6 CE, Tiberius was to lead at least eight legions (VIII Augusta and XIII Gemina from Pannonia, XV Apollinaris and XX Valeria Victrix from Illyricum, XXI Rapax from Raetia, XIV Gemina and XVI Gallica from Germania Superior and an unknown unit) against king Maroboduus of the Marcomanni in Czechia; at the same time, I Germanica, V Alaudae, XVII, XVIII and XIX were to move against Czechia as well, attacking it along the Elbe. It was to be the most grandiose operation that was ever conducted by a Roman army, but a rebellion in Pannonia obstructed its execution. For three years, the Romans were fighting to restore order on the Balkans, and the Thirteenth was one of the active units.