Syria–Türkiye border

From Sèvres to the railway

Syria was an Ottoman province from 1516 until the empire collapsed in 1918. The Treaty of Sèvres of 1920 would have put the border far to the north, leaving Aintab, Urfa and Mardin to Syria, but it was never enforced inside Turkey and was replaced by the Treaty of Lausanne in 1923.^[1]

The line came instead from an agreement between France, which held the mandate for Syria, and Turkey on 20 October 1921. For a long central stretch it follows the Baghdad Railway: the track as far as Nusaybin stays in Turkey, so the border runs just south of the rails. A convention of 1926 and a protocol of 1929 fixed the rest of the line east to the Tigris, whose deepest channel marks the last stretch wherever the river moves.^[1]

“The frontier will follow the Baghdad Railway, of which the track as far as Nisibin will remain in Turkish territory.”^[1]

Hatay

The 1921 agreement also gave the district of Alexandretta, inside French-mandated Syria, a special autonomous regime.^[1] Turkey began pressing for it in 1936, and in 1939 France handed it over, alongside a Franco-Turkish treaty of friendship on the eve of the Second World War. France defended the move at the League of Nations as a way to avoid a Turkish attack on Syria.^[3] The Sanjak of Alexandretta, now Turkey’s Hatay province, was transferred on 23 July 1939, and a new line was marked along the Karasu, Afrin and Orontes rivers to the sea.^[1]

Syria has never formally recognised the transfer, and its official maps long showed Hatay as Syrian, but its governments rarely raised the issue. In the 2000s, as relations improved, the two countries planned a shared Friendship Dam on the Orontes, which would in effect have acknowledged the border; work stopped when the Syrian uprising began in 2011.^[3]

A tomb over the border

The 1921 treaty also let Turkey keep the tomb of Suleyman Shah, grandfather of the Ottoman Empire’s founder, as Turkish territory inside Syria, guarded by Turkish soldiers. In February 2015, with Islamic State fighters nearby, about 100 Turkish military vehicles crossed near Kobane, brought the guards home and removed the remains, to be reburied at Eshme, closer to the border and under Turkish army control.^[4]

War, a wall and three operations

When Syria’s war began, refugees crossed in huge numbers: by 2020 Turkey had hosted more than 4 million.^[5] Turkey built a wall covering 764 km of the 911 km border, finished in June 2018, against Islamic State and against the Kurdish People’s Protection Units (YPG), which Turkey considers an extension of the outlawed PKK.^[2]

Turkey also sent its army across. Operation Euphrates Shield took al-Bab from Islamic State, Operation Olive Branch took Afrin from the YPG, and Operation Peace Spring, launched on 9 October 2019, was aimed chiefly at the area between Tal Abyad and Ras al-Ayn.^[5] A Turkish analyst described the aim as holding a 30 km strip along the border east of the Euphrates.^[5]

After Bashar al-Assad fell on 8 December 2024, Syrians began going home. By the end of April 2026 UNHCR estimated that about 640,000 had returned from Turkey, more than from any other country, and about 2.3 million Syrians remained there.^[6]