Legio II Parthica was a Roman legion levied by emperor Lucius Septimius Severus in 197 AD, for his campaign against the Parthian Empire, hence the cognomen Parthica. The legion was still active in the middle of the 4th century. The legion's symbol was a centaur.
Together with its twin legions I Parthica and III Parthica, the second Parthian legion was levied for the attack on the eastern frontier. The campaign was a success and Ctesiphon, the Parthian capital was taken and sacked. After this war, the second returned to Italy, and was stationed near Rome in the Alban mountains. Since it was not garrisoning a Roman province, their functioned both as a reserve that could be used in afflicted parts of the Empire, as well as a security element against possible internal rebellions. Emperors in the 3rd century were very likely to have problems with usurpers and Severus, by stationing the II Parthica near the capital, was aware of it.
Nevertheless, the legion served in the Severan campaign in Britain of 208/211 AD and afterwards, under Caracalla against the Germanic tribe of the Alamanni in 213. Next, the legion was again sent to Parthia and their commander Macrinus was responsible for Caracalla's murder in that region in 217. In the following year, however, the legion abandoned Macrinus and sided with Heliogabalus, who would become emperor instead. This new usurper of usurpers awarded the legion with the cognomina Pia Fidelis Felix Aeterna (forever faithful, loyal and lucky).
In 231 the legion fought under Alexander Severus against the Sassanid dynasty and returned with the emperor to the Germania provinces. It was at Mainz (Roman Moguntiacum) when Alexander was assassinated in 235. In the following fight for the power, the II Parthica sided with Maximinus Thrax. In 238, the Roman senate declared Maximinus persona non grata and nominated Gordian III as emperor. Maximinus then marched on Rome to fight for his rights, taking the II Parthica, among other legions, with him. What happened next is a good example of the political power of the legions in the 3rd century. The II Parthica weighted the chances of its commander and, concluding that supporting him was not a good move, they killed Maximinus before he could harass the senate. As a reward, they were pardoned by supporting a public enemy and allowed to return to their camp in the Alban mountains.
In the next decades they were used as reinforcements in several provinces within the empire and continued to be used as pawns in the constant battles for the imperial throne of the 3rd century. The last record of the II Parthica is in the Tigris frontier in the middle of the 4th century, just before a major Roman defeat by the Persians.
See also: List of Roman legions