The XIIth Imperial Legion is one of Garlemald's armies in Final Fantasy XIV. Led by Crown Prince Zenos yae Galvus, the XIIth Imperial Legion is known for its brutality. Recently victorious in putting down a rebellion in Doma, the legion was also given command of Ala Mhigo following the supposed death of Gaius van Baelsar and fall of the XIVth Imperial Legion.
Under its merciless Legatus, power is valued above all else, and the prince has little use for those who will not "hunt" their own prey, often killing his own soldiers should they fail to meet his expectations. Because the legion controls two annexed territories, Zenos remains in Gyr Abania as its viceroy, while Doma is commanded by his appointed viceroy, Yotsuyu goe Brutus.
Unofficially, and somewhat scornfully, the Crania Lupi are also a part of the XIIth Legion, under the command of Fordola rem Lupis.
During the events of Final Fantasy XIV: Stormblood, the Scions of the Seventh Dawn, the Ala Mhigan Resistance and the Eorzean Alliance battle with the XIIth Legion is the mission to free Ala Mhigo from the empire. They soon know defeat after facing the might of Zenos, forcing them to regroup and plan a new strategy. Resolving to force the XIIth Legion to fight on two fronts, the Scions travel to Doma to reignite the flames of rebellion and free the nation, thereby giving the Eorzean Alliance and the Resistance a better chance at defeating Zenos.
The Scions free Doma after rallying its people under Hien Rijin and the Doman Liberation Front, forcing members of the XIIth in Doma to retreat. Taking this chance, the Eorzean Alliance and the Resistance conduct their bold campaign to force the XIIth Legion out of Ala Mhigo: Rhalgr's Beacon. After suffering many casualties and contending with a powerful primal, the Warrior of Light defeats Zenos, who commits suicide.
With their Legatus believed dead, the XIIth Legion retreats in earnest, leaving Ala Mhigo free from the empire. What became of the Legion following Zenos's defeat is unknown, but it's likely they retreated back to Garlemald.