On 29 September 1913 (16 September Old Style), in Constantinople, the Ottoman Empire and the Kingdom of Bulgaria sign the Treaty of Constantinople — the separate peace ending the Second Balkan War between the two states after the Treaty of Bucharest had excluded the Ottomans.

Bulgaria acknowledges Ottoman gains of Adrianople (Edirne), Kırklareli and Didymoteicho; the Empire cedes the port of Dedeagach (Alexandroupoli) to Bulgaria. Evacuation and exchange of territories, demobilisation within three weeks, release of prisoners and resumption of diplomatic and economic ties follow.

The Eastern Thrace frontier largely fixes the modern line between European Turkey, Bulgaria and Greece.

In the First World War the two states were Central Powers allies; the borders were later reaffirmed at Lausanne.

For the Balkan Wars, 29 September 1913 marks the Ottoman–Bulgarian peace.

The text is available in diplomatic collections (TTK, English translations).

The Treaty of Constantinople of 29 September 1913 remains the Ottoman–Bulgarian peace milestone.

Image: Istanbul / Thrace; Wikimedia Commons. Cropped to 16:9.

Source consulted: Treaty of Constantinople (1913). Treaty text: Treaty of Peace Bulgaria–Turkey 1913 (text).