The Danube forms most of the border between Romania and Bulgaria. For much of its course, the river runs along the two countries’ frontier before continuing north past Silistra, where the boundary turns across the Dobruja region toward the Black Sea.
The border’s modern outline emerged after the Russo-Turkish War and was revised by several treaties, including the Treaty of Bucharest and the Treaty of Craiova. The river boundary is crossed by bridges, ferries, and road links, including the New Europe Bridge between Vidin and Calafat and the Danube Bridge between Ruse and Giurgiu.
A common mix-up is the Prut, which forms much of Romania’s border with Moldova, not Bulgaria. The Tisza is associated with Hungary, Serbia, Slovakia, and Ukraine, while the Dniester mainly concerns Ukraine and Moldova. The Danube is Europe’s second-longest river and reaches the Black Sea through its large delta in Romania and Ukraine.