Although the monks of the monastery of Rolduc operated a mine beginning in the Middle Ages, large-scale mining only really got under way in the early 20th century in the province of Limburg. At the peak of its production, the Limburg mines produced some 12 million tons of coal a year and 55,000 em ployees found work in this industry. Since 1958, mining has declined as a consequence of the increasing use of natural gas.
Historical Dictionary of the Netherlands. EdwART. 2012.