Greek Thrace (Thraki) is often called Western Thrace to differentiate the Greek portion of the large ancient region that is now divided by Greece, Bulgaria, and Turkey. The area of Greek Thrace is 8,578 square kilometers. The eastern border with Turkey is formed by the Evros River (called the Maritsa by Bulgarians and the Meric by Turks), which flows southward into the Aegean Sea after flowing eastward across southern Bulgaria. The Nestos River flows from southern Bulgaria to define the regional border between Thrace and Macedonia to the west. No major rivers flow through Thrace.
Most of northern Thrace is dominated by the southern tier of the Rhodopes (Rodopi) Mountains, most of which lie in Bulgaria. The Thracian Plain runs along the shore of the Aegean Sea and along the Maritsa Valley to the east. This alluvial plain is cut into three parts by plateaus extending southward from the Rhodopes to the Aegean Sea. The three plains are the most agriculturally significant area of Thrace, and the region's three provinces are defined by their location.
The plain in Evros, the easternmost province, is a traditionally productive agricultural area, enriched by the fertile soil of the Maritsa Valley and by abundant water from the Evros River and its tributaries. The plains in the other two Thracian provinces, Rodopi and Xanthi, also feature rich soil that is especially favorable for tobacco cultivation.
Unlike Greece's other maritime regions, most of Thrace's coastline is smooth, broken only at the mouth of Lake Vistonis, which is actually a bay of the Aegean Sea located on the boundary of the prefectures of Rodopi and Xanthi. The lake is the spawning area for commercially important fish species. The mountainous and sparsely populated island of Samothrace, about sixty kilometers offshore in the Aegean Sea, is administered as part of the prefecture of Evros. The statue that became known as the Winged Victory of Samothrace, now a treasure of the Louvre Museum in Paris, was discovered on the island.
Thrace was the only region of Greece in which Muslims were allowed to remain according to the population exchanges prescribed by the Treaty of Lausanne in 1923. Today the Muslim population is concentrated in the provinces of Rodopi and Xanthi. Most of the region's residents are ethnically Greek, however, and many descend from Greek refugees who returned from Turkey in the Greek expatriation phase of the Lausanne agreement