Legio duodevigesima (Eighteenth Legion, spelled XVIII or XIIX) was a Roman legion levied by the future Augustus around 41 BC. The legion was, along with two others, destroyed in the Battle of Teutoburg Forest (September 9, 9). The legion's symbol and cognomen are unknown.
This legion was probably created to deal with Sextus Pompeius, the last opponent of the second triumvirate, garrisoned in Sicily and threatening Rome's grain supply. It was probably one of the eight legions Augustus promised Mark Antony for his campaign against the Parthians, but never delivered.
Following the defeat of Antony and Cleopatra in the battle of Actium (31 BC), the legion was stationed in Gaul. In the end of the 1st century BC, the XVIIIth was sent to the Germania provinces in the Rhine to take part in the enormous army led by Drusus and later Tiberius. In 5, the provinces were pacified. In 7, Publius Quinctilius Varus was assigned governor.
In September 9, Arminius, leader of the Cheruscan allies, reported a rebellion in the Rhine area. Without suspecting the information received, Varus took his three legions, the XVIII along with XVII and XIX, and headed west. On 9 September, near modern Osnabrück, the Cheruscii led by Arminius ambushed the governor's army. All three legions were destroyed in what is known as the Battle of Teutoburg Forest and their eagle standards lost.
After their destruction, the Romans never used two of the three legion numbers (XVII and XIX) again. However, the emperor Nero would raise a new XVIII legion, which was raised for his planned Egyptian campaign. Nero's plan was never realized, and four cohorts saw service in Judea during the first revolt of AD 69–70, while the other six cohorts were involved in the Revolt of the Batavi in the same year. The legion was shortly thereafter disbanded by Vespasian.