If no arrangement on a principle of give and take is made between them, the road to the East, which from the point of view of the Germanic powers lies through Serbia, will sooner or later inevitably be forced open, and the independence, first of Serbia, Montenegro, and Albania, and later of Bulgaria and Greece, will disappear, _de facto_ if not in appearance, and both materially and morally they will become the slaves of the central empires. If the Balkan League could be reconstituted, Germany and Austria would never reach Salonika or Constantinople. 2 _The Balkan Peninsula in Classical Times_ 400 B.C.–A.D. 500. In the earlier historical times the whole of the eastern part of the Balkan peninsula between the Danube and the Aegean was known as Thracia, while the western part (north of the forty-first degree of latitude) was termed Illyricum; the lower basin of the river Vardar (the classical Axius) was called Macedonia. A number of the tribal and personal names of the early Illyrians and Thracians have been preserved. Philip of Macedonia subdued Thrace in the fourth century B.C. and in 342 founded the city of Philippopolis. Alexander’s first campaign was devoted to securing control of the peninsula, but during the Third century B.C. Thrace was invaded from the north and laid waste by the Celts, who had already visited Illyria. The Celts vanished by the end of that century, leaving a few place-names to mark their passage. The city of Belgrade was known until the seventh century A.D. by its Celtic name of Singidunum. Naissus, the modern Nish, is also possibly of Celtic origin. It was towards 230 B.C. that Rome came into contact with Illyricum, owing to the piratical proclivities of its inhabitants, but for a long time it only controlled the Dalmatian coast, so called after the Delmati or Dalmati, an Illyrian tribe. The reason for this was the formidable character of the mountains of Illyria, which run in several parallel and almost unbroken lines the whole length of the shore of the Adriatic and have always formed an effective barrier to invasion from the west. The interior was only very gradually subdued by the Romans after Macedonia had been occupied by them in 146 B.C. Throughout the first century B.C. conflicts raged with varying fortune between the invaders and all the native races living between the Adriatic and the Danube. They were attacked both from Aquileia in the north and from Macedonia in the south, but it was not till the early years of our era that the Danube became the frontier of the Roman Empire.