Its name is derived from the name of an Illyrian tribe called the Dalmatae, which lived in the central area of the eastern coast of the Adriatic Sea.

It encompassed the northern part of present-day Albania, much of Croatia, Bosnia and Herzegovina, Montenegro, and Serbia, thus covering an area significantly larger than the current Croatian and Montenegrin region of Dalmatia.

The region which ran along the coast of the Adriatic Sea and extended inland on the Dinaric Alps was called Illyria by the Greeks.

[6] Due to Octavian having subdued the more inland region of Pannonia (along the mid-course of the River Danube), the Romans changed the name of the coastal area to Dalmatia.

In 6–9 AD, there was a large scale rebellion in the province of Illyricum, the Bellum Batonianum (Batonian War).

[9][full citation needed] However, Šašel-Kos notes that an inscription attests a governor of Illyricum under the reign of Claudius (41–54 AD) and in a military diploma published in the late 1990s, dated July 61 AD, units of auxiliaries from the Pannonian part of the province were mentioned as being stationed in Illyricum.

[14] The Croatian historian Aleksandar Stipčević writes that analysis of archaeological material from that period has shown that the process of romanization was rather selective.

[15] In 454 Marcellinus, a military commander in Dalmatia, rebelled against Valentinian III, the Roman emperor in the West.

In 488 Zeno, the new emperor of the east, sent Theodoric the Great, the king of the Ostrogoths, to Italy so as to depose Odoacer.

Zeno also wanted to get rid of the Ostrogoths, who were Roman allies and were settled in the eastern part of the empire, but were becoming restless and difficult to manage.