Narrow-gauge railways in Serbia
Most Serbian railway lines were built as a result of an expansion of railway networks by Austro-Hungarians. Several 760 mm (2 ft 5+15⁄16 in) gauge railways were planned to link the extensive narrow-gauge railways in the Austro-Hungarian Empire with those in Bosnia and Herzegovina.
Source: Wikipedia — Narrow-gauge railways in Serbia (CC BY-SA 4.0)