The foundation of the German Customs Union was the trigger for the Industrial Revolution. When trade barriers between German states were abolished in 1834 this gave rise to an attractive market in goods. Demand for coal rose quickly and mining areas boomed. The villages in the Ruhrgebiet rapidly merged to become crowded towns and cities as new collieries and ironworks sprung up out of the ground - at the start with capital from the prospering economies of Belgium and Great Britain and also with thousands of foreign workers. Essen developed into a new industrial centre. The first deep mine was sunk to reach the rich supplies of coal beneath the surface there. The Krupp ironworks manufactured steel for the railways and an increasing number of cannons for the State. As such it was the germ cell for an gigantic empire. The Hoesch firm, later also one of the steel giants in the Ruhrgebiet, began producing railway lines in Eschweiler near Aachen. Ironworks in Neunkirchen und Burbach sprung up along the River Saar and in 1873 the Völklingen ironworks went into operation.