Bulgaria–Serbia border

Two new states, 1878

Serbia and Bulgaria were both under Ottoman rule for centuries. The Ottomans took Sofia in 1382 and beat the Serbs and their allies at the Battle of Kosovo in 1389.^[1]

Revolts in the 1870s led to the Russo–Turkish War of 1877–78. The Treaty of San Stefano (3 March 1878) made Serbia fully independent, with extra land around Niš, and created a large Bulgaria reaching from the Danube to the Aegean.^[1] The Great Powers made Russia think again. The Treaty of Berlin (13 July 1878) recognized Serbia as independent and set up a smaller, self-governing Bulgaria stretching east from the Timok river, still under the Ottoman Sultan.^[1]

The line was tested in 1885. After Eastern Rumelia declared unification with Bulgaria on 18 September, Serbia's King Milan demanded Bulgarian land and declared war on 14 November. Bulgaria won the decisive battle at Slivnitsa (17–19 November) and pushed the Serbian army back into Serbia.^[3] The Treaty of Bucharest (3 March 1886) put the old border back but left Bulgaria and Eastern Rumelia united.^[3]

Wars and the Treaty of Neuilly

In March 1912 Serbia and Bulgaria signed a secret alliance to drive the Ottomans out of the Balkans and share Macedonia. They won the First Balkan War, then fell out over the spoils. In June 1913 Bulgaria attacked the Serbian and Greek armies, lost the Second Balkan War, and gave up most of its Macedonian claims in the Treaty of Bucharest (10 August 1913).^[1]

Bulgaria sided with Germany in the First World War and lost again. Today's line was set by Article 27 of the Treaty of Neuilly-sur-Seine, signed by Bulgaria and the Allied Powers on 27 November 1919. It fixed Bulgaria's frontier with the new Kingdom of the Serbs, Croats and Slovenes, which became Yugoslavia.^[1][4] Much of it follows “the old frontier between Bulgaria and Serbia”, but in several places the treaty drew a new line “to be fixed on the ground”.^[1]

The line mostly follows mountain crests and watersheds. The US Geographer listed the exceptions as small areas taken from Bulgaria, among them the land around Tsaribrod, Bozica and Bosilegrad.^[1] An International Boundary Commission with members from Bulgaria, the Serb–Croat–Slovene kingdom, Japan, Italy, Britain and France marked it on the ground in 1920–22, with numbered pillars each visible from the next.^[1]

In the Second World War Bulgaria again joined Germany and ran large parts of Yugoslav Macedonia. The 1947 Paris Peace Treaty put the 1919 boundary back.^[1] In 1972 the US Geographer reported no open official disputes over where the line runs.^[1]

“thence to a point on the Tsaribrod–Sofiya road immediately west of its junction with the road to Kalotina”^[1]

Tsaribrod and Bosilegrad

Bulgaria often calls the land it gave up under Neuilly the Western Outlands. In Serbia that means the towns of Dimitrovgrad and Bosilegrad, both mainly ethnic Bulgarian in 2017. The term also covers Strumica, now in North Macedonia.^[4] In the 1950s Yugoslavia renamed Tsaribrod Dimitrovgrad, after Georgi Dimitrov, Bulgaria's first communist leader.^[4]

Restoring the old name has been on the Bulgarian minority's agenda for decades. In November 2017 activists from the town asked for Tsaribrod back at a press conference in Sofia. Bulgaria's parliamentary press service reported that Serbian President Aleksandar Vučić saw no problem with it “as long as this is what people want”. In Bulgaria the idea was controversial, and the opposition Socialists warned it could worsen relations with Serbia.^[4]

Kalotina and Corridor X

The main crossing is Kalotina on the Bulgarian side and Gradina on the Serbian side, one of Europe's busiest land border crossings. It sits on Pan-European Transport Corridor X, one of the main land routes between Western Europe, the Middle East and Asia. Summer holidays and freight regularly back traffic up for miles.^[2]

The site has little room to grow. On 9 July 2026 the interior ministers, Ivan Demerdzhiev and Ivica Dačić, met at Kalotina to sign an agreement for a second, shared checkpoint called Kalotina 2 – Gradina 2. It will be on Bulgarian land near the existing crossing, and both countries' officers will check travellers there together.^[2]