Cycle tour 2021 - Belgium/5: Art in the Zonneberg cave (Maastricht)

(This report is not complete and probably contains inaccuracies because the guide went too fast).

10 Oct - Maastricht:
Visit to Zonneberg 'caves' and museum under St Peter's Mountain in Dutch-Belgian border area.
About four kilometres outside Maastricht lies the Sint-Pietersberg nature reserve. I had cycled alongside it for quite some time on Saturday from the Belgian border village of Kanne, but I had no idea that in the lap of that elongated hill is an untold expanse of tunnels whose construction began as early as the 13th century.

Actually, it is not a cave system, as the passages were dug out by human hands. The 'block breaking' started in the 13th century. Maastricht had been granted city rights at the end of the 12th century and a city wall had to be built. It was decided to carve the necessary stone blocks from the Sint-Pietersheuvel. This was the start of this impressive corridor system.

125 million ago, this marl mound lay on the seabed, resulting in a lot of limestone deposits from shellfish. This resulted in marl with a high limestone content, ideal for making high-quality cement. Since the Middle Ages, this marl was exploited by four owners who each owned a section of Mount St Peter. In total, 220,00 galleries were carved between the 13th and 20th centuries, covering a total length of 230 km.

Part of this corridor system was destroyed because ENCI (Eerste Nederlandse Cement Industrie), which had a marl quarry of 145 hectares and 60 metres deep installed. That is now shut down and one can visit the 60-metre-deep quarry.

The corridor system we walked over about 4 km (in the Dutch 'Zonneberg' part) was full of inscriptions, some of which dated as far back as the Middle Ages. There are also many drawings on the walls there was even a real 'museum' inside with a full-size copy (roughly, anyway) of the Night Watch by Rembrandt. There were also drawings of old and contemporary celebrities in the museum.

When no more corridors could be cut in the early 20th century, interest arose to open the impressive underground structure to the public. An entrance ticket then cost 2 guilders. That is now equivalent to the price of a fancy dressing gown or hotel stay with all the trimmings. I.e. only for the wealthy....

Since this was an interesting target audience consumption-wise, some companies began to put up advertising ads in the corridors. They thus sponsored the restoration and maintenance of the open corridors. These were the predecessors of today's billboards in cities and along roads.

During World War II, the corridor system served as an air-raid shelter with a capacity for a total of 42,000 people. Three thousand refugees volunteered to live here because they feared that the Germans would blow up the bridges over the Meuse River, making it impossible for them to escape. I saw pumping stations, evacuation plans and arrows to 'toilets'. So many people having to do their business underground, that must have caused quite a stink, I thought. Not so. The toilets were very rudimentary but efficient: marl is extremely permeable to water, so the small need was immediately sucked up by the underground. For major needs, a deep trench was dug against the wall with partitions and curtains into which each person could drop his/her cargo. After the poop, no bag but a big shovel of sand over it. When the trench was full, they dug a new one and moved the partitions. After all, there were plenty of trenches.

For the mental well-being of the refugees, there were three chapels of different faiths. Near the Christian chapel were drawings of all stages of the Stations of the Cross.

There was also a bakery with 3 ovens and chimneys, but it never produced bread. They were used by the most vulnerable refugees to warm themselves, as they included elderly people and pregnant women. Some babies were even given birth underground.

What were the corridors still used for?

• In 1769, a Reformed synod was held of the so-called 'lightning children' (swear name)
• To smuggle: tobacco from Belgium to the Netherlands and milk, butter and cheese from the Netherlands to Belgium.
• During the war, Dutch Jews were led underground as far as Belgium, from where they could escape further to France. During dark nights, they were lowered into Dutch territory through a vertical shaft via a rope ladder, where a guide waited for them. They left the cave by a small smuggling hole on the Belgian side.
• During the war, large works from the Rijksmuseum, Kroller-Muller and other museums were safely stored in the underground passages in the northern section. Rembrandt's real Night Watch was also taken there.
• Museum function: the original museum was right up against ENCI's concession area. The security perimeter was too small and holes appeared in the museum wall, allowing people to enter the museum from outside. Weather and wind also gained access this way. The museum became very damaged and in early 1990 it was repaired with a larger perimeter. The Night Watch drawing was restored only very recently.
•  There is a statue of a (prehistoric) turtle.
•  An image of a 'Mosasaurus'. That was a prehistoric dino 13 to 16 metres long. It had no legs but fins. In 1767, the first skeleton was found in the marl. On a hard bone, the saw sounded differently than in soft marl, and so the block breakers found a bone 1.5 m long and teeth 10 cm big. A fossil collector, one Dr Hofman, took care of these finds, which dated back many millions of years. It was then the period of the French Revolution and these finds contradicted the creation story in the Bible. So the Anti-Catholic revolutionaries made grateful use of it in their discourse against the church, and the first skeleton was transferred to France, where it still stands today at the Natural History Museum. A total of four skeletons were found in the belly of Mount St Peter. And how did this critter get its name? Mosa coming from Maas and saurus was used because of its resemblance to a dino.
• Every winter, 3,500 bats hibernate here. Perhaps winged offspring of the Mosasaurs?

This underground structure is well worth a guided visit. Most of the photos of the artworks in the Flickr album include a brief explanation.