Bulgaria is a country in Southeastern Europe. It is bordered by Romania to the north, Serbia and North Macedonia to the west, Greece and Turkey to the south, and the Black Sea to the east. The capital and largest city is Sofia; other major cities are Plovdiv, Varna and Burgas. With a territory of 110,994 square kilometres (42,855 sq mi), Bulgaria is Europe's sixteenth-largest country. One of the earliest societies in the lands of modern-day Bulgaria was the Neolithic Karanovo culture, which dates back to 6,500 BC. In the 6th to 3rd century BC the region was a battleground for Thracians, Persians, Celts and ancient Macedonians; stability came when the Roman Empire conquered the region in AD 45. The Eastern Roman, or Byzantine, Empire lost some of these territories to an invading Bulgar horde in the late 7th century. The Bulgars founded the First Bulgarian Empire in AD 681, which dominated most of the Balkans and significantly influenced Slavic cultures by developing the Cyrillic script. This state lasted until the early 11th century, when Byzantine emperor Basil II conquered and dismantled it.