Legio V Iovia was a Roman legion

Roman legion

A Roman legion normally indicates the basic ancient Roman army unit recruited specifically from Roman citizens. The organization of legions varied greatly over time but they were typically composed of perhaps 5,000 soldiers, divided into maniples and later into "cohorts"...

 levied by Diocletian

Diocletian

Diocletian |latinized]] upon his accession to Diocletian . c. 22 December 244  – 3 December 311), was a Roman Emperor from 284 to 305....

 in the end of the 3rd century, and was still in service at the beginning of the 5th century. The cognomen

Cognomen

The cognomen nōmen "name") was the third name of a citizen of Ancient Rome, under Roman naming conventions. The cognomen started as a nickname, but lost that purpose when it became hereditary. Hereditary cognomina were used to augment the second name in order to identify a particular branch within...

 of the legion refers to Jupiter, to whom Diocletian (also known as Iovianus, "the man like Jupiter") was devoted and identified.

The V Iovia was stationed, together to her sister legion VI Herculia

Legio VI Herculia

Legio VI Herculia was a Roman legion levied by Diocletian in the end of the 3rd century, and was still in service at the beginning of the 5th century...

, in Pannonia Secunda

Pannonia Secunda

The Pannonia Secunda was one of the provinces of the Roman Empire. It was formed in the year 296, during the reign of emperor Diocletian. The capital of the province was Sirmium...

, a new province

Roman province

In Ancient Rome, a province was the basic, and, until the Tetrarchy , largest territorial and administrative unit of the empire's territorial possessions outside of Italy...

 created with the segmentation of the old Pannonia

Pannonia

Pannonia was an ancient province of the Roman Empire bounded north and east by the Danube, coterminous westward with Noricum and upper Italy, and southward with Dalmatia and upper Moesia....

 province. The legion received the ordinal "Fifth" because in Pannonia there were already four legions. The purpose of the legion, having her permanent camp in Bononia

Bononia

Bononia is the Roman name of several cities, including:* Bologna, Italy* Boulogne-sur-Mer, France* Vidin, Bulgaria* Banoštor, Serbia...

 and an advanced castellum

Castellum

A castellum is a small Roman detached fort or fortlet used as a watch tower or signal station. The Latin word castellum is a diminutive of castra , which in turn is the plural of castrum ; it is the source of the English word "castle".The term castellum was also used to refer to a settling or...

 in Onagrinum, was to protect the imperial residence of Diocletian in Sirmium

Sirmium

Sirmium was a city in ancient Roman Pannonia. Firstly mentioned in the 4th century BC and originally inhabited by the Illyrians and Celts, it was conquered by the Romans in the 1st century BC and subsequently became the capital of the Roman province of Lower Pannonia. In 294 AD, Sirmium was...

 (Illyricum

Praetorian prefecture of Illyricum

The praetorian prefecture of Illyricum was one of four praetorian prefectures into which the Late Roman Empire was divided.The administrative centre of the prefecture was Sirmium , and, after 379, Thessalonica...

).

The Notitia Dignitatum

Notitia Dignitatum

The Notitia Dignitatum is a unique document of the Roman imperial chanceries. One of the very few surviving documents of Roman government, it details the administrative organisation of the eastern and western empires, listing several thousand offices from the imperial court down to the provincial...

 locates the legion still in Illyricum at the beginning of the 5th century.

It is possible that some men from this legion and from the VI Herculia formed the Jovians and Herculians

Herculians

The Jovians and Herculians were the senior palatine imperial guard units of the Emperors of the late Roman Empire and the early Byzantine Empire from the 290s until the 7th century.-History:...

, the new imperial bodyguard of Diocletian. If this identification is correct, V Iovia men had the appellative martiobarbuli, since they were expert in throwing small darts, carried by five in the inside of their shields.