After the success of Septimius Severus against Parthia, I and III Parthica remain in the region in the camp of Singara to avoid following rebellions and attacks from the Parthian Empire. The newly creataed province of Mesopotamia was to be an exception: it was ruled by men of equestrian order, not senators.
Legionaries from I Parthica were usually sent to other provonces, namely Lycia, Cilicia and Cyrenaica.
See also: List of Roman legions, Roman legion