Much of the region south of the Danube River was known as Noricum. The western uplands region between the upper Rhine River, the lower course of the Inn River, and the Bavarian and subalpine plateau was known as Rhaetia, an area which also included parts of modern-day Germany and Switzerland. The plains region in the east and southeast was known as Pannonia and included areas in present-day Hungary and Slovenia. The Romans invaded all three regions about 15 bc and made them provinces of the empire. Under Roman control, the provinces eventually became outposts for offensive and defensive action against various barbarian tribes. To a large extent Roman strategy was based on the fact that the region contains important passes through the Eastern Alps and thus commands vital transportation arteries between northern, southern, western, and eastern Europe. One of the first Roman military posts in the region was Vindobona (now Vienna), which was located on the site of a Celtic settlement on the edge of the Eastern Alps and on an arm of the Danube. Vindobona became an important strategic crossroad for two main trade routes and for numerous roads leading into the fertile basin of Niederösterreich. Carnuntum (now Petronell), east of present-day Vienna, was another important Roman center in the area.

In the territories of Austria the first traces of human settlement date from the Lower Paleolithic Period. The archaeological material becomes richer and more varied for subsequent periods, giving evidence of several distinct cultures succeeding one another or coexisting. The Austrian site of Hallstatt gave its name to the principal culture of the Early Iron Age (c. 800–450 BC). Celtic tribes invaded the eastern Alps about 400 BC and eventually founded the kingdom of Noricum, the first “state” on Austrian territory known by name. In the west, however, the ancient race of Raetians was able to maintain its seat. Then, attracted by the rich iron resources and the strategic importance of the region, the Romans began to assert themselves. After an initially peaceful penetration during the last two centuries BC, Roman troops finally occupied the country about 15 BC, and the lands as far as the Danube became part of the Roman Empire, being allotted to the Roman provinces of Raetia, Noricum, and Pannonia.

June 28, 1914, the heir to the Austro-Hungarian throne, Archduke Francis Ferdinand, and his wife were assassinated in the Bosnian capital of Sarajevo by Gavrilo Princip, a Serbian nationalist. After receiving German assurances of support, the Austro-Hungarian foreign office sent a harsh ultimatum to the Serbian government, holding it responsible for the assassination and requiring its total acceptance of Austria-Hungary’s demands within three days. Despite a conciliatory reply that accepted all but two of the demands, and mediation efforts by the European powers, Austria-Hungary declared war on Serbia on July 28. Germany’s declaration of war on Russia and France in early August transformed the conflict into World War I. Austro-Hungarian military activity during the first year of the war was concentrated against Russia and Serbia. In May 1915 Italy, which had declared its neutrality in 1914, left the Triple Alliance and entered the war on the side of the Allies.