The section between Alexandroupoli (formerly "Dedeagatch") and Svilengrad was opened in 1874 by the Chemins de fer Orientaux (CO) when the entire Thrace was part of the Ottoman Empire. The part between Pythio and Svilengrad was part of the CO main line from Istanbul to western Europe. After World War I and the subsequent Greek-Turkish War from 1919 to 1922, and finally peace in the form of the Lausanne treaty, the Chemins de fer Orientaux (CO) ended up having a network straddling Turkey and Greece. This created operational difficulties, each country having now its own set of rules and regulations, currencies, and languages. In order to resolve this situation, the CO decided to split itself into two companies: one for the Greek part, one for the Turkish part of the railway.