Legio XIII Gemina (The 13th Legion)
Sestertius minted in 248 by Philip the Arab to celebrate Dacia province and its legions, V Macedonica and XIII Gemina. Note the eagle and the lion, V's and XIII's symbols, in the reverse.
Active	57 BC to sometime in the 5th century AD
Country	Roman Republic/Roman Empire
Allegiance	Rome
Branch	Army
Type	Roman legion (Marian)
Role	Infantry assault (some cavalry support)
Size	Varied over unit lifetime. Approx. 3,500 fighting men + support at the time of creation.
Part of	Roman legion (Marian)
Garrison/HQ	Roman Dacia (89 AD onwards)
Patron	Julius Caesar, Augustus Caesar, Roman Emperors
Mascot	Roman Lion
Engagements	Gallic Wars (58-51 BC) Battle against the Nervians (57 BC) Battle of Gergovia (52 BC) Battle of Alesia (52 BC) - uncertain Battle of Dyrrhachium (48 BC) Battle of Pharsalus (48 BC) Battle of Thapsus (46 BC) Battle of Munda (45 BC) Battle of Actium (31 BC) 1st and 2nd Battles of Bedriacum (69 AD) Vexillationes of the 13th particicpated in many other campaigns.
Commanders
Current commander	N/A
Notable commanders	Julius Caesar Marcus Salvius Otho Marcus Antonius Primus

Legio XIII Gemina (the twin legion), was levied by Julius Caesar on 57 BC, before his attack against the tribe of the Belgae. There are still records of the XIII Gemina in Dacia (modern Romania) in the beginning of the 5th century. The legion symbol was a lion.

In Caesar's Gallic wars, the Thirteenth was present in the battle against the Nervians and the siege of Gergovia. When the senate refused Caesar his second consulship and civil war was about to begin, the Thirteenth was the legion that accompanied Caesar across the Rubicon river and into Italy. They remained faithful to Caesar in the civil war against Pompey, being present in the battle of Munda (45 BC) and in the African campaign. In 45 BC Caesar disbanded the legion, giving the veterans farmlands in Italy.

In 41 BC the legion was reconstituted by Augustus to deal with Pompey's sons' rebellion in Sicily. After the war against Mark Antony and the battle of Actium, the Thirteenth was reinforced with veteran legionaries from other legions and acquired the cognomen Gemina. Augustus then sent this legion to Burnum (modern Knin), in Illyricum, a Roman province in the Adriatic Sea. In 16 BC they were transferred to Emona (now Ljubljana), Pannonia, where they dealt with local rebellions.

After the disaster of the battle of the Teutoburg Forest in AD 9, the legion was sent as reinforcements to Augusta Vindelica (Augsburg), Germania Superior to prevent further attacks from the Germanic tribes. Emperor Claudius sent them back to Pannonia around 45; the legion camped at Poetovio (modern Ptuj, Slovenia).

In the year of the four emperors, XIII Gemina supported first Otho and then Vitellius, two of the defeated emperors, fighting in the two Battles of Bedriacum.

In 89 Domitian transferred the legion to Dacia (in Apulum, modern Alba Iulia, Romania) to garrison the province from their camp in Vienna. They remained in this camp until the 5th century, according to Notitia Dignitatum, although some vexillationes participated in several foreign campaigns.

• A fictionalized account some of the actions of Legio XIII Gemina during the struggle between Julius Caesar and the Optimates faction under Pompey can be seen in the joint HBO/BBC television production Rome.

• Roman legion
• List of Roman legions

• livius.org account
• LEG XIII GEM, Austrian re-enactment group
• Legio XIIII Gemina Martia Victrix (Roman Military Research Society)