Thrace (; ; ; ) is a geographical and historical region in Southeast Europe. It is split among Bulgaria, Greece, and Turkey, which is bounded by the Balkan Mountains to the north, the Aegean Sea to the south, and the Black Sea to the east. It comprises southeastern Bulgaria (Northern Thrace), northeastern Greece (Western Thrace), and the European part of Turkey (East Thrace). The region's boundaries are based on that of the Roman Province of Thrace; the lands inhabited by the ancient Thracians extended in the north to modern-day Northern Bulgaria and Romania and to the west into the region of Macedonia. Etymology The word Thrace was first used by the Greeks when referring to the Thracian tribes, from ancient Greek Thrake (Θρᾴκη), descending from Thrāix (Θρᾷξ). It referred originally to the Thracians, an ancient people inhabiting Southeast Europe. The name Europe first referred to Thrace proper, prior to the term vastly extending to refer to its modern concept. The region could have been named after the principal river there, Hebros, possibly from the Indo-European arg "white river" (the opposite of Vardar, meaning "black river"), According to an alternative theory, Hebros means "goat" in Thracian. In Turkey, it is commonly referred to as Rumeli, "Land of the Romans", which was the name traditionally given by Turkic societies to the Byzantine Empire and Orthodox Christians. Mythology In terms of ancient Greek mythology the name appears to derive from the heroine and sorceress Thrace, who was the daughter of Oceanus and Parthenope, and sister of Europa. Geography Borders The historical boundaries of Thrace have varied. The ancient Greeks employed the term "Thrace" to refer to all of the territory which lay north of Thessaly inhabited by the Thracians,<ref>{{cite book |first=Thomas |last=Swinburne Carr |title=The history and geography of Greece |publisher=Simpkin, Marshall & Company |page=56 |url=https://archive.org/details/historyandgeogr00carrgoog |year=1838 }}</ref> a region which "had no definite boundaries" and to which other regions (like Macedonia and even Scythia) were added. In one ancient Greek source, the very Earth is divided into "Asia, Libya, Europa and Thracia". As the Greeks gained knowledge of world geography, "Thrace" came to designate the area bordered by the Danube on the north, by the Euxine Sea (Black Sea) on the east, by northern Macedonia in the south and by Illyria to the west. This largely coincided with the Thracian Odrysian kingdom, whose borders varied over time. After the Macedonian conquest, this region's