Bulgaria
Bulgaria occupies a portion of the eastern Balkan peninsula, bordering five countries—Greece and Turkey to the south, Macedonia and Serbia to the west, and Romania to the north. The land borders have a total length of , and the coastline has a length of . Its total area of ranks it as the world's 105th-largest country. Bulgaria's geographic coordinates are 43° N 25° E. The most notable topographical features are the Danubian Plain, the Balkan Mountains, the Thracian Plain, and the Rhodope Mountains. The southern edge of the Danubian Plain slopes upward into the foothills of the Balkans, while the Danube defines the border with Romania. The Thracian Plain is roughly triangular, beginning southeast of Sofia and broadening as it reaches the Black Sea coast.
Balkans
In pre-classical and classical antiquity, this region was home to Greeks, Illyrians, Paeonians, Thracians, Dacians, and other ancient groups. The Achaemenid Persian Empire incorporated parts of the Balkans comprising Macedonia, Thrace, Bulgaria, and the Black Sea coastal region of Romania between the late 6th and the first half of the 5th-century BC into its territories. Later the Roman Empire conquered most of the region and spread Roman culture and the Latin language, but significant parts still remained under classical Greek influence. The Romans considered the Rhodope Mountains to be the northern limit of the Peninsula of Haemus and the same limit applied approximately to the border between Greek and Latin use in the region (later called the Jireček Line). However large spaces south of Jireček Line were and are inhabited by Vlachs (Aromanians), the Romance-speaking heirs of Roman Empire. The Bulgars and Slavs arrived in the 6th-century and began assimilating and displacing already-assimilated (through Romanization and Hellenization) older inhabitants of the northern and central Balkans, forming the Bulgarian Empire. During the Middle Ages, the Balkans became the stage for a series of wars between the Byzantine Roman and the Bulgarian Empires.