The Jiu Valley ( ]) is a region in southwestern,Transylvania, Romania, in Hunedoara county, situated in a valley of the Jiu River between the Retezat Mountains and the Parâng Mountains. The region was heavily industrialised and the main activity was coal mining, but due to low efficiency, most of the mines were closed down in the years following the collapse of Communism in Romania. For a long time the place was called Romania's biggest coalfield.