Noricum had been incorporated into the Roman Empire in 16 BCE.

For a long time the Noricans had enjoyed independence under princes of their own and carried on commerce with the Romans.

In 48 BCE they had taken the side of Julius Caesar in the civil war against Pompey.

In 16 BCE, having joined with the Pannonians in invading Histria, they had been defeated by Publius Silius, proconsul of Illyricum.

Thereafter, Noricum was called a province, although it was not organized as such and remained a kingdom with the title of regnum Noricum, yet under the control of an imperial procurator.Under the reign of Emperor Claudius (41–54) the Noricum Kingdom ias ultimately incorporated into the Roman Empire apparently without offering resistance.

It is not until the reign of Antoninus Pius that the Second Legion, Pia (later renamed Italica) is stationed in Noricum, and the commander of the legion becomes the governor of the province.

Under Diocletian (245–313), Noricum is divided into Noricum ripense ("Noricum along the river", the northern part southward from the Danube), and Noricum mediterraneum ("landlocked Noricum", the southern, more mountainous district).

The dividing line runs along the central part of the eastern Alps.

Each division is under a praeses, and both belong to the diocese of Illyricum in the Praetorian prefecture of Italy.

It is in this time that a Christian serving as a military officer in the province suffers martyrdom for the sake of his faith, later canonized as Saint Florian.The Roman colonies and chief towns are Virunum (near Maria Saal to the north of Klagenfurt), Teurnia (near Spittal an der Drau), Flavia Solva (near Leibnitz), Celeia (Celje) in today's Slovenia, Juvavum (Salzburg), Ovilava (Wels), Lauriacum (Lorch at the mouth of the Enns, the ancient Anisus).Knowledge of Roman Noricum has been decisively expanded by the work of Richard Knabl, an Austrian epigrapher of the nineteenth century.