During the war between Macrinus and Elagabalus, the Battle of Immae in 218 took place. The Praetorians were to face the famous Legio II Parthica. This battle was unusual from the beginning: Cassius Dio reports that the emperor ordered his army to fight without armour. Despite the lack of armour, the praetorians forced the army of the usurper, but for some reason, Macrinus chickened out and fled the battlefield, thanks to what Elagabalus finally won (Cassius Dio LXXVIII 37).
So what was unusual about this clash? Well, Felsonius Verus, aquilifer of legio II Parthica, instead of having a banner ending with the image of a golden eagle, he carried a banner with a cage in which a real eagle was placed. it can be seen in its unique tombstone relief. Felsonius died during the war between Gordian III and the Sassanids.