The Ioviani were created by soldier Emperor Diocletian (284-305 AD) as an elite guard unit. The name Ioviani derives from Iuppiter, the patron god of the legion. Later on, they became part of the Palatina Legions of the new Constantinian army as elite regiments led personally by the emperor. They served under emperor Valentinian the Great as Ioviani Seniores in his aggressive campaigns on the Rhine Frontier, taking part in the Battle of Solicinium in 368 AD.
They also served in the province of Britannia under Comes Theodosius against the Picts, the Franks and the Saxons. In the year 388 AD, the Ioviani fought again in Germany, losing their commander Heraclius in battle. They took part in the Battle of the Frigidus in 395 AD. They served under the Magister Militum Flavius Stilicho and in this period they were headquartered in Pisa, Tuscany. They fought against the rebellion of the Comes Gildo in North Africa alongside the Herculiani Seniores. At the beginning of the 5th century, the Ioviani Seniores were probably still based in Pisa and were one of the last units to dissolve in the west, remaining loyal to the emperor till the very end. The Ioviani were one of the most senior Palatina Legions in the west. They were proficient in the throwing of plumbata, a form of lead-weighted dart carried by heavy infantry. Their shield crest was a red eagle on a blue field. Before engaging in battle, the Ioviani would perform the barritus, a roman war chant of germanic origin that consisted in a crescendo of low pitched noises enhanced by putting the mouth close to the shield. They fought as heavy infantry, armed with a long spatha and an oval shield. They probably also carried short spears.