Legio III Herculia: one of the legions of the later Roman empire. Its name means "the legion dedicated to Hercules".
This legion was created by the emperor Diocletian (284-305). It was called after Diocletian's colleague, the emperor Maximianus, who often called himself Herculius, "the man like Hercules". The date of the creation is unknown, but was probably at the beginning of the joint reign of the two emperors.
III Herculia was probably created to defend a province, but was later added to the field army of Illyricum. The original province is not known, but may have been Raetia. At the end of the fourth century, III Herculia was still part of the Illyrian field army. It is mentioned as the twin of III Italica.