The railway started in 1865 at the port town of Poti on the Black Sea. The railway reached Zestaponi in 1871 and T'bilisi in 1872. The contractor for this part of the line was Messrs G.B. Crawley and Co.; the resident engineer was Edward Preston who had previously been at work in North Wales. This may account for the interest shown by this railway in Welsh mountain railways and narrow-gauge steam locomotives running on the north Wales Festiniog Railway. A branch line was built to Kutaisi, branching from Brotseula, in 1877. In 1883, the railway was completed to Baku. Once the railway was completed to Baku, freight trains carrying oil went from Baku to Poti to be shipped to other cities in Russia via the Black Sea. During the Russian-Ottoman war from 1877–1878, the Russian Empire gained territory into Anatolia from the Ottoman Empire after defeating them during the Battle of Kars. This new territory included the fortress city of Kars. In 1887, a branch line was built to Tkibuli. In 1894, a branch line, splitting of at Khashuri, was built to Borjomi. Kars was a strategic city for the Russians in Anatolia, so in 1899 the railway built a branch line from T'blisi to Kars. The Transcaucasus Railway was connected to the rest of the Russian system in 1900, when the line from Baku to Makhachkala was completed. A railway connection through the Caucasus mountain range to connect to the Russian system was considered as early as the 1890s, but the implementation of the Caucasian Pass Railway only started in the 1980s and was abandoned after a few years. In 1902, the narrow gauge Borjomi to Bakuriani Railway was built to serve the skiing community in the region. In 1913, the railway was extended from Kars to Sarıkamış; the border of the Russian Empire and the Ottoman Empire at the time. When World War I broke out in 1914, the Russian Empire sided with the Allied powers while the Ottoman Empire sided with the Central Powers making the two empires enemies. After the Erzerum Offensive, Russia gained control city of Erzurum. To support campaigns further into Ottoman territory, a 750 mm (2 ft 5+1⁄2 in) gauge railway was built from Sarıkamış to Erzurum in 1916 and extended to Yeniköy later the same year. Russia had to stop fighting in the war because of the Russian revolution of 1917, that led to the dissolution of the Russian Empire.