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. History Before the 19th century The region was populated since ancient times, being part of Dacia. During the Middle Ages, the inhabitants of the Jiu Valley lived in huts spread along the mountains, and often near the river, and the main activity was shepherding. Until the early 19th century the region remained sparsely populated due to its geographical isolation (being surrounded by mountains). 19th century and early 20th century The development of coal mining started in the Jiu Valley about 160 years ago, around the middle of the 19th century, when Hungarian, German, Czech and Polish workers were brought from all parts of the Habsburg Empire to work in the coal mines. Romanian miners from other regions, such as Baia Mare or the Apuseni Mountains, were also brought to work in the Jiu Valley. During the late 19th century, the region started to strongly develop itself, economically and culturally, through a flourishing industry based on mining. The Jiu Valley, being situated in Transylvania, was part of the Austro-Hungarian Empire until the 1918 Union of Transylvania with Romania. During World War I, the area was the site of heavy fighting between Romanian forces on one side and German and Austro-Hungarian forces on the other side. The first battle ended in an important, albeit temporary defensive victory for the Romanians, nevertheless the Central Powers succeeded to break through the Romanian defences here in November 1916. Mining continued to dominate the economy in the 20th century, but the region also experienced social unrest, notably the Lupeni Strike of 1929. The mines were privately owned until 1948, when all private companies were nationalized by the Communist government. The Jiu Valley during the Communist regime As part of Romania's reparations to the Soviet Union for its wartime alliance with Germany, the Romanian coal mines were nationalized and converted into joint Soviet-Romanian companies (SovRoms). These Sovroms continued for about ten years. The Jiu Valley expanded rapidly in the second half