Mine Cockerill — Grube Katzenberg Esch-sur-Alzette · Canton Esch-sur-Alzette · Luxembourg

The Katzenberg concession at Esch-sur-Alzette was granted on 8 August 1881 to Charles and Jules Collart, brothers who owned the foundries at Steinfort and Rodingen, for a term of fifty years at an annual rent of 18,750 francs. The Collart brothers were from Dommeldingen and were among the earliest industrialists in the area. Their first mine tunnel under this concession was not at Katzenberg but at a location called Eisekaul.

In 1887 the brothers relocated the mining operations to the foot of the Katzenberg. The construction of the buildings on the lower Katzenberg site was directed by the mining engineer André Koch. Production grew steadily: by 1913 output had reached 216,000 tonnes.

After the First World War the Steinfort foundry and the Katzenberg mine were sold to the French Société des Mines de la Loire. In 1921 they were acquired by the Belgian company Athus-Grivegnée. In 1928 that company merged with others and was renamed S.A. Angleur-Athus.

During the Second World War Luxembourg was occupied by Germany and the mine was placed under forced administration; on 1 April 1943 it was integrated into the Gewerkschaft Lützelburg. After the end of the war, in 1946, S.A. Angleur-Athus merged with S.A. John Cockerill, the Belgian steel and industrial concern originally founded by the English-born industrialist John Cockerill in 1817. From this merger the mine derived the name by which it is commonly known today.

Toward the end of the 1950s the mining operations were largely mechanised: scrapers and loading machines were acquired, an ore crusher was installed between the brown and black ore deposits, and a conveyor belt replaced earlier transport methods, with temporary ore storage in silos before dispatch by truck. The mine closed on 31 December 1967, after more than eighty-five years of operation. The remaining ore reserves requiring concessions, estimated at 21 million tonnes, were allocated among ARBED, HADIR, and MMR, and the majority of the workforce transferred to those companies.

The Ellergronn valley fell silent. In 1970 the former mine buildings were sold to a construction company, but no development was carried out. The Luxembourg state purchased the entire area in 1986 and 1988 to establish a nature reserve.

On 8 May 1991 the founding meeting of the volunteer association Initiativ fir d'Erhaalen vun de Cockerillsgebaier zu Esch-Uelzecht am Ellergronn took place, symbolically occupying the mining site. In the following years clearing work and provisional waterproofing of the old forge roof were undertaken. In November 1995 the association was renamed Entente Mine Cockerill, and in December 1996 it was registered as a non-profit organisation in the Memorial, the official Luxembourg gazette, with Frédéric Georges, the last director of the Katzenberg mine, serving as honorary president.

The preserved site includes the pithead washroom (Salle des Pendus), the old forge, two mine tunnel entrances, a small museum showing fossils, minerals, mining tools, and artefacts from the iron industry, and the former mine grounds within the Ellergronn nature reserve. The nature reserve forms part of the Natura 2000 network. The museum and site are registered on the European Route of Industrial Heritage.

The adjacent Ellergronn nature conservation centre is housed near the museum.