After a couple decades of believing there was something odd about the area. Finally, in 1867, a railway line was dug that cut through 25 mining shafts. It is the origin and, discovery of the site Spiennes Mons.

Covering more than 100 ha (250 acres), it is the largest and earliest concentration of ancient mines in Europe.

Brief synthesis
Covering essentially an agricultural area. The Neolithic Flint Mines of Spiennes occupy two chalk plateaus located south-east of the city of Mons. Though below, underground, the site is an immense network of galleries dug out by almost 10,000 year old neolithic populations.
The area houses the biggest and earliest concentration of ancient mines of north-west Europe. In operation for many centuries, the areas origins still remain moderately illustrative in the development and adaptation of modern mining techniques. In order to exploit large deposits of materials the site was used to dig down shafts of .8 to 1.2m in diameter to a depth of about 16m. Populations could pass thru blocks of flint about 2m length. They used a technique called ‘striking’. Where they would free the blocks from below with the support of a chalk wall, shoring up the block, removing of the wall, and the props and thus lowering of the block. Where they could then get it up and out the shaft, break down and analyze further for flintknapping.

Largest & longest neolithic flint mine
In the neolithic period, from the last 3rd of the 5th millenium, until the 1st half of the 3rd millenium (almost 2000 years). The site was used for extensive flint mining.

Tree falling tools, for huts, canoes and more
Production aimed at the manufacture of axes to fell trees; and, long blades to be used, and transformed into tools.

Where did they live while mining?
A camp was discovered at the site comprising two irregular concentric pits at a distance of 5 to 10m. The archaeological artifacts discovered are characteristic of the Michelsberg culture (neolithic culture in the center of Europe) discovered in the mining sector. It was a giant working mans camp site.

Metal ages
After the metal ages, the area turned to agricultural land. In the 1700s, armies of Louis XIV dug out a pit of 3m in depth accompanied by an earthen wall. By the 1800s they started manufacturing of gun flints again. Now if your in the Belgium or northern France area. Definitely worth checking out.

Bibliography: C. Guillaume, Ph. Lipinski & A. Masson: Les mines de silex néolithiques de la Meuse dans le contexte européen. Musées de la Meuse, Sampigny 1987. (in French)

Collet, H. (2004). Les mines néolithiques de Spiennes : état des connaissances et perspectives de recherche (PDF). Section 10: The Neolithic in the Near East and Europe (in French). Oxford: Archaeopress. ISBN1-84171-653-7.