The Chemins de fer Orientaux (English: Oriental Railway; Turkish: Rumeli Demiryolu or İstanbul-Viyana Demiryolu) (reporting mark: CO) was an Ottoman railway company operating in Rumelia (the European part of the Ottoman Empire, corresponding to the Balkan peninsula) and later European Turkey, from 1870 to 1937.

The reporting mark was CO. By the second half of the 19th century, the once powerful and dominant Ottoman Empire was declining greatly.

However, due to the rise of nationalism in the Balkans, mostly provoked by Russia, the Ottoman Empire was slowly losing its control over the area.

The Crimean War had just ended and gave the aging Empire a slight break against Russian influence over the Balkans.

The Sultanate in Istanbul looked to strengthen its sovereignty in the region and help its declining economy during the short peace.

Trade by sea was dominated by the British naval monopoly, so the Sublime Porte had to look at other ways of transport.

Railways showed their effectiveness in western Europe and the Ottomans sought to bring this technology into the empire.

A trunk line such as that would allow easier deployments of troops in the European part of the Empire and would open up many new trade opportunities with western Europe.

The decision for a railway was finalized and Abdülaziz awarded a concession to Van der Elst and Cie, a Belgian construction company, on 31 May 1868, with the help of André Langrand-Dumonceau.

he ran into financial difficulties and could not continue construction of the line, so the Sultanate cancelled the concession on 12 April 1869.

Hirsch then founded the Imperial Turkish European Railway, headquartered in Paris, to build the line in 1869.

The company hired Wilhelm von Pressel, from the Austrian Southern Railway, to be the chief engineer of the project.

Following a government change the same year, the new Grand Vizier Mahmud Nedim Pasha started to renegotiate the concession to reduce the budget of constructing the line because of the Empire's growing financial problems.

Under the new agreement, Hirsch would continue to manage ongoing construction, but the Ottoman government would supervise in building new lines.

The longest and most important of these lines were Constantinople to Belovo via Edirne and Filibe, with branches to Dedeağaç and Yambol.

In 1881, King Milan awarded a concession to Paul Eugène Bontoux, a French entrepreneur, to construct a railway from Belgrade to Vranje via Nis.

Once complete, the SDZ would have full ownership of the railway between Nis and Belgrade but operation of the line would be done by the CO via trackage rights.

[5] One of the most famous trains in history, the Orient Express, started her first run from Paris to Istanbul on 1 June 1889.