Caspian Sea
The Caspian has characteristics common to both seas and lakes. It is often listed as the world's largest lake, although it is not a freshwater lake. It contains about 3.5 times more water, by volume, than all five of North America's Great Lakes combined. The Caspian was once part of the Tethys Ocean, but became landlocked about 5.5 million years ago due to plate tectonics. The Volga River (about 80% of the inflow) and the Ural River discharge into the Caspian Sea, but it has no natural outflow other than by evaporation. Thus the Caspian ecosystem is a closed basin, with its own sea level history that is independent of the eustatic level of the world's oceans.
Trans-Caspian railway
Construction began in 1879 of a narrow-gauge railway to Gyzylarbat in connection with the Russian conquest of Transcaspia under General Mikhail Skobelev. It was rapidly altered to the standard Russian gauge of five feet, and construction through to Ashkabad and Merv (modern Mary) was completed under General Michael Nicolaivitch Annenkoff in 1886. Originally the line began from on the Caspian Sea, but the terminus was later shifted north to the harbour at Krasnovodsk. The Railway reached Samarkand via Bukhara in 1888, where it halted for ten years until extended to Tashkent and Andijan in 1898. The permanent bridge over the Oxus (Amu-Darya) was not completed until 1901, and until then trains ran over a rickety wooden construction that was often damaged by floods. As early as 1905, there was a train ferry across the Caspian Sea from Krasnovodsk to Baku in Azerbaijan. The Tashkent Railway connecting the Transcaspian Military Railway with the network of other Russian and European railways was completed in 1906.