Illyria, northwestern part of the Balkan Peninsula, inhabited from about the 10th century bc onward by the Illyrians, an Indo-European people. At the height of their power the Illyrian frontiers extended from the Danube River southward to the Adriatic Sea and from there eastward to the Šar Mountains.
The Illyrians, bearers of the Hallstatt culture (see Hallstatt), were divided into tribes, each a self-governing community with a council of elders and a chosen leader. A strong tribal chieftain, however, could unite several tribes into a kingdom. The last and best-known Illyrian kingdom had its capital at Scodra (modern Shkodër, Albania). One of its most important rulers was King Agron (second half of the 3rd century bc), who, in alliance with Demetrius II of Macedonia, defeated the Aetolians (231). Agron, however, died suddenly, and during the minority of his son, his widow, Teuta, acted as regent. Queen Teuta attacked Sicily and the Greek colonies of the coast with part of the Illyrian navy. Simultaneously, she antagonized Rome, which finally sent a large fleet to the eastern shores of the Adriatic. Although Teuta submitted in 228, the Illyrian kingdom of the interior was not destroyed, and a second naval expedition was sent against Illyria in 219. Philip V of Macedonia aided his Illyrian neighbours and thus started a protracted war that ended with the conquest of the whole Balkan Peninsula by the Romans. The last Illyrian king, Genthius, surrendered in 168 bc.
The Roman province of Illyricum stretched from the Drilon River (the Drin, in modern Albania) in the south to Istria (modern Slovenia and Croatia) in the north and to the Savus (Sava) River in the east; its administrative centre was Salonae (near present-day Split) in Dalmatia. With the extension of the Roman Empire along the Danube River valley, Illyricum was divided between the provinces of Dalmatia and Pannonia.
Under the empire Illyria enjoyed a high degree of prosperity. It was traversed by a Roman road, and Illyria’s ports served as important trade and transit links between Rome and what is now eastern Europe. Copper, asphalt, and silver were mined in parts of the region, and Illyrian wine, oil, cheese, and fish were exported to Italy.
Since the semiautonomous clansmen of the Illyrian highlands were hardy warriors, it was inevitable that the emperors should recruit them to serve with the Roman legions and even the Praetorian Guard. When in the 3rd century bc the empire began to be threatened by the barbarian peoples of what are now eastern and central Europe, Illyricum became a principal military bulwark of Rome and its culture in the ancient world. Several of the most outstanding emperors of the late Roman Empire were of Illyrian origin, including Claudius II Gothicus, Aurelian, Diocletian, and Constantine the Great, most of whom were chosen by their own troops on the battlefield and later acclaimed by the Senate.
In ad 395 the empire was finally divided, and Illyria east of the Drinus River (the Drina, in modern Yugoslavia) became part of the Eastern Empire. Between the 3rd and the 5th century it was devastated by the Visigoths and the Huns, who, however, left no lasting mark on Illyria. But the Slavs, who started their incursions into the Balkan Peninsula in the 6th century, had by the end of the 7th century transformed the ethnic structure of all the Illyrian-speaking territories. Croatia, Serbia, Dalmatia, Bosnia, Montenegro, and parts of Macedonia lost their Illyrian language and were thoroughly Slavonized, so that only the Albanians remain as direct descendants of the ancient Illyrians. For the later history of the region, see Balkans.