[Lucius Cornelius Sulla]

In the source it says the findings are from the first century BC, at which time Illyria was a Roman Province. It was part of Julius Caesar’s Proconsulate province, along with Gaul on the Italian side of the Alps, and Gaul across the Alps. It appears to have been pacified by his time.

[SunkenCiv]

Illyria and Dalmatia must have been quiet throughout most of the imperial times, and were under Roman control before big Julie's time. Most of the major battles between Caesar and Pompey were fought in the countryside. It was part of the major overland route to the east, Diocletian built his retirement cottage there, and from the pics I've seen, it's kinda pretty. The Byzantines didn't seem to have that much trouble regaining it each time they lost control due to barbarian invasions and whatnot.

[Verginius Rufus]

Shakespeare's Twelfth Night is set in Illyria.

There's a recent book in English, The Illyrians by John Wilkes (1992). The archaeological museum in Split, Croatia, has some Illyrian items on display, including a helmet.

The coastal areas were indeed part of the province assigned to Julius Caesar--Roman involvement in Illyria dates back to the late 3rd century--but the interior was not fully subdued until the reign of Augustus. In fact there was a major uprising against the Romans between A.D. 6 and 9 involving a large part of present-day Bosnia and parts of Croatia. That uprising may have contributed to the success of the German uprising of A.D. 9 led by Arminius (who defeated Quinctilius Varus at the battle of the Teutoburg Forest).