Border convention at Didymoteicho

A British chronology of the war records under 9 September 1915 the signing at Didymoteicho (PL) (Dimetoka in Turkish, Dimotika in Bulgarian) of a border convention between Turkey and Bulgaria. The sources do not confirm this date. The convention was signed three days earlier in Sofia, together with the Bulgarian–German treaty of alliance. On 9 September the first reports of the course of the new border were only just reaching the press of the Entente countries. The official British chronology published in 1918 noted under this date that the final text of the convention had not yet been signed. The matter returned to Didymoteicho two weeks later: according to the American envoy in Sofia, Lewis Einstein, the Turkish delegates put their signatures to the final protocol at the railway station in that town only when news arrived of the Bulgarian mobilisation decree.

A strip of land on the Maritsa

The convention was signed on 6 September by the Ottoman minister in Sofia, Ali Fethi Bey, later Fethi Okyar, and the Bulgarian Prime Minister Vasil Radoslavov. Turkey ceded to Bulgaria the lands west of the Tundzha and the Maritsa: the Edirne suburb of Karaağaç with its railway station, the small town of Cisri Mustafa Paşa, Didymoteicho and a narrow strip along the river as far as its mouth near Enez. Bulgaria also received a strip one and a half to two kilometres wide on the left, eastern bank of the Maritsa, so that the whole river lay within its borders. In all this came to about 2,600 square kilometres. According to the Turkish historian Ahmet Yiğit, some 65,000 people lived there, most of them Muslim Turks. The convention guaranteed them the same rights as Bulgarian Muslims had.

The railway was what mattered most. After the Balkan Wars Bulgaria had gained the Aegean coast with the port of Dedeagach (PL), but the railway line from its interior to that port ran for a stretch through Karaağaç and Didymoteicho on Turkish territory. After the border change the whole route from Sofia to the Aegean ran through Bulgarian land. In return Turkey could use for five years the section of railway that remained on the Bulgarian side. The exact course of the border on the ground was to be fixed by a commission including representatives of Germany, Austria-Hungary and Sweden, and the handover of territory was to begin on 11 October.

The price of Bulgaria

For a long time the Turks would not hear of concessions. They agreed to the border change only under German pressure and in August, when after the new Allied offensive at Gallipoli they began to run short of ammunition. Supplies from Germany could reach Constantinople only through Serbia and Bulgaria. On 17 August the War Minister İsmail Enver asked the German Chief of the General Staff, Erich von Falkenhayn, whether a blow against Serbia was in preparation. He was told that it depended on Bulgaria entering the war, and that in turn on a Bulgarian–Turkish agreement. The negotiations with the Bulgarians were conducted by the President of the Ottoman parliament, Halil Bey (Menteşe), and at the end of August the two sides reached agreement. The concessions, however, were to take effect only if Bulgaria bound itself to the Central Powers by a military convention.

In Constantinople the government approved the convention by a provisional law on 13 September, and from the following day it was formally in force. Many officers received it with indignation. İsmet, later President İnönü of Turkey, recalled that the news of the cession of the land on the Maritsa filled them with anger. Enver tried to reassure him that the final borders would in any case be settled only by the end of the war. In some documents the authorities wrote of Didymoteicho as “temporarily ceded to the Bulgarians”.

For Bulgaria this was the first tangible gain from its agreement with the Central Powers. According to Bulgarian sources, the country then reached the largest area in its modern history. For Turkey it was the cost of opening the road to Germany. Two weeks later Bulgaria announced mobilisation, and after the conquest of Serbia in the autumn of 1915 the overland route from Germany to Constantinople was opened.