Zonneberg Caves

SEE THE CITY FROM A DIFFERENT ANGLE

English brochure to use during a guided tour in the Zonneberg Caves

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Welcome INTRODUCTION DRAWINGS The origins & safety of limestone

Second First BAKERY The Flower World War Catholic chapel, SWW

Medallion Crucifix Advertise- The Muses ments

The block Flint Bats more breaker INFORMATION

Welcome to the Zonneberg caves On behalf of Maastricht Underground and Natuurmonumenten (Society for the Preservation of Nature Monuments in the Netherlands) we extend to you a warm welcome to the Zonneberg Caves.

You will visit the Zonneberg Caves as part of a huge network of around 22,000 underground tunnels dug into this hill. The tunnel walls of this enormous maze carry the signs of >

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MENU chopping and cutting by block breakers as well as many writings, drawings and sculptures. Much of this was brought about for tourism one hundred years ago. These signs of chopping and cutting are the silent witnesses of hard labour around the extraction of marlstone in this area for 700 years. >

In this document we describe the highlights you may encounter during the guided tour. Your guide will point out these highlights, allowing you to look up all relevant information in this document. Some of the stops are not listed in this document and some stops described in this document are not part of the tour. The guide will have to be selective in painting a varied and full picture of events that happened at this location through the centuries. On various guided tours you will be visiting different locations! Please feel free to ask questions. We hope you will enjoy your guided tour!

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Safety MENU

First of all we ask your attention for some safety aspects: • Gasoline lamps can be hot! Do you, or someone near you, carry such a lamp? In that case, please make sure that no one can touch the top of the lamp.

• some floors are uneven. Please take care when walking on such floors.

• please stay with your group and follow the directions given by your guide. Do not wander off through the tunnels in the unlikely event that your guide is incapacitated, but stay put until help has arrived. Help is on its way for sure; no further action is required.

• please do not touch the walls or any objects on the walls.

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Introduction MENU

The temperature in this network of tunnels is a constant 11°C / 52°F (summer and winter, day and night). The humidity is around 98%. The rock also holds a lot of water. This is also the reason why most of the drawings were produced using charcoal; paint would go mouldy and peel off the walls. Charcoal can remain on the walls as a powdery coating for hundreds of years as long as nobody touches it. We must therefore ask you NOT to scratch the walls or to touch the drawings!

Many inscriptions can be admired on the walls, the oldest of which in these tunnels dates from 1551. In the early 1900s, it was mainly local artists who came here to give free rein to their creativity on the walls and hoped in this way to attract new clients and commissions. The competition between the four different cave networks led the owners of the caves to invite artists to create artworks in the caves. >

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A touristic publication dating from 1898 describes the tour of the caves in great detail. These excursions were at the time exclusively available to the well-to-do. An admission ticket cost ‘two guilders for the first visitor and 50 cents for every additional visitor.’ To put this into perspective, an overnight stay at a hotel with breakfast cost just one guilder at the time.

After the Second World War, mass tourism really started to grow. A number of educational illustrations were added during that period, along with even more drawings, carvings, and sculptures.

The climate in these caves also attracts many hundreds of bats in the winter months, coming here to hibernate. >

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During the Second World War, various facilities were set up in these tunnels in order to be able to house almost 50,000 people in them for a period of time. However, Maastricht was ultimately never on the front line of the war, so the large-scale evacuation never proved necessary. Nonetheless, you will undoubtedly encounter signs of this evacuation plan during this tour.

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Drawings MENU

Most of the drawings that you will see were produced using charcoal. This is due to the climate inside the hill and its tunnels. The limestone is also permeated with moisture, so any paint used would go mouldy and peel off, especially as the paint used in the past was made using egg yolks. Charcoal is an inert and porous material that remains well preserved on the surface of the walls as a layer of powder. Some drawings, such as that of Ahasverus (the Wandering Jew) and that of the dragon, are more than a hundred years old; but if you were to rub your fingers over it, it would be easily erased. By not touching the drawings, we can ensure they will adorn these walls for hundreds of years more. >

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The drawing of Ahasverus - a cobbler, also known as the Wandering Jew - was produced in the early 1900s by Messrs Van der Veur and Simays. It is a wonderful example of the deeply-rooted religious traditions in this southern part of the Netherlands, a source of inspiration for many artists. >

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The drawing of the dragon was produced in 1907 by T. Bottema, who studied here in Maastricht at the city’s school of drawing and later became known for his illustrations in works including the Dik Trom series of Dutch children’s books and the children’s bible. His best-known design is that for an insurance company, Nationale Nederlanden: a lady with an umbrella, a gentleman with a walking stick, and a dog.

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The origins of limestone This drawing dating from the early 1900s gives an impression of how things looked here around 70 million years ago. The mammoth (on the right) didn’t evolve until many millions of years later, and the various dinosaurs (in the middle) are also not correct in this picture. >

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In that period, the end of the Cretaceous period, the area that is now Western Europe lay submerged under a fairly shallow subtropical sea. The nearest coastline was 50 km to the east. The sea creatures and other creature that lived here included the Mosasaurus. This reptile was the largest and hungriest creature swimming around in this area. It grew up to 17 metres in length, and ate everything it encountered, including other mosasauri.

If you also consider that the Cretaceous Sea extended from Ireland to Ukraine, you can imagine the huge amount of calcium-rich deposits that accumulated. >

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20 meters / 66 ft. Soil

10 meters / 33 ft. Limestone

10 meters / 33 ft. Tunnels

60 meters / 197 ft.

Jeker Meuse

The layer in which these tunnels were created is chiefly made of remnants of algae, foraminifera, single-celled organisms, and other tiny creatures, resulting in a homogeneous layer of rock that makes an excellent building stone. The elephant on the left of the drawing has been drawn next to the dinosaurs as a reference point, to give visitors an idea of the size of these creatures.

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Second MENU World War

In the final years of the Second World War, preparations were made in these tunnels for the potential evacuation of around 50,000 inhabitants of Maastricht. In the event that Maastricht should find itself on the front line, sandwiched between the Nazis on one side of the Meuse and the Allies on the other, a large proportion of the population was to make use of this evacuation plan. The main initiator and designer of this plan was the Maastricht architect Harrie Koenen. The plan included a large number of facilities including a bakery, a hospital including operating theatres, a psychiatric ward, toilets, electric lights in the main tunnels, a public address system, three water pumping stations with large water storage facilities (see photo), two Catholic chapels, and one Protestant chapel, amongst many other features. >

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In the end, the official large-scale evacuation never took place, as Maastricht was liberated from the east by the American troops and was never on the front line. Nevertheless, towards the end of the war, a few thousand people did make use of the tunnels for ten days. These were mainly people who lived in the city centre, where the bridges were the targets of various bombardments. All kinds of provisions such as crates containing medicines, blankets, crockery etc. were not used because the plan was never officially executed. In any case, it became clear during those ten days that the plan would not have worked adequately anyway; the toilets stank and were unhygienic, the straw storage areas were swarming with rats and mice, and not all facilities were operational yet. With hindsight, there are plenty of reasons to be glad that the end of this troubled period for Maastricht finally came on 14 September 1944, after four years, four months, and four days of war.

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First Catholic chapel Second World War The evacuation plan dating from the Second World War also featured places of worship; two Catholic chapels, and one Protestant chapel. You are now at the first Catholic chapel, with the altar and the cross on top. On the wall to the left of the chapel is a depiction of ‘Our Lady of Perpetual Help,’ modelled on a Polish icon. >

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This drawing was created in a different way from most of the other drawings; the surface was first blackened, and the parts that were to be made white were then scratched away (a technique known as sgraffito).

Actual church services were held in this chapel, and during the war years a child was even baptized here. A number of Stations of the Cross are shown on the walls of the tunnel leading straight to the chapel. There should be fourteen of them, but there are only eight and a half. Viewed from the chapel, you can see an unfinished drawing on the left wall of this tunnel. This drawing marks the moment at which the national anthem was played over the public address system to announce the liberation of the city. People of course stopped with what they were doing and normal life resumed. Next to this half-finished drawing, you can also see a number of empty spaces that were never used.

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Bakery Second World War This bakery formed part of the evacuation plan from the Second World War. Five hot-air ovens were to be installed, with a combined maximum capacity of 10,000 loaves per day. Ovens no. 1 (straight in front of you) and no. 2 (to the right) are still accessible. Oven no. 3 is positioned behind oven no. 2. The war ended before ovens 4 and 5 could be installed. These ovens were multi-burners; >

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MENU they could be heated from below with tree branches, coal, wood, paper, peat, and any other kind of combustible material that was available. These ovens each had two baking sheets positioned one above the other which were heated by means of the hot air channelled into the hot oven.

The round tubes at the top were used to heat water. Water pumping station no. 1 is located near this bakery. Some of the pumped water was conveyed to these ovens with the aid of an extra pump situated in the alcove between the two ovens. The water was heated by pumping it through the round tubes.

These ovens would have been in use 24 hours a day, and the smoke would have escaped via the enormous 35-metre-tall factory chimney that you can see above oven no. 2. >

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Above the ground, on the plateau beside the Lichtenberg farmstead (Hoeve Lichtenberg), you can see about 2 metres of concrete pipe sticking out of the field. This is the top of the chimney.

The only drawing visible on the wall in this section reminds us of the fact that Mrs Regina Beks gave birth to her sixth child, her son Frits, here during the last few days of the war. The first-aid post had relocated to the bakery as it was the only place that could be kept relatively warm. The drawing was produced at the request of Frits Beks who visited the Zonneberg tunnel network on the occasion of his fiftieth birthday.

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The flower Second World War In his own words, written on the back of this photograph of the flower: ‘Sgraffito of marl wall / coated with black bone meal / scraped using piece of electrical conduit.’ This drawing may have been created here as a kind of signpost for the guides, young people from the nearby Veldeke college, who had been given an intensive training course on the basis of a diagrammatic map teaching them the way through the illuminated main tunnels. >

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If the necessity arose, they had to lead the sheltering people outside, or from outside to one of the 27 zones into which the tunnel network was divided. The city’s residents were allocated to one of these zones depending on the city district in which they lived.

The main tunnels were given names. We still use those names today, including Alphaweg (Alpha road), KLM-weg (KLM road), and Bloemenweg (Flower road), part of Route E, the walls of which still bear a red letter E.

From ‘the Flower,’ you have a clear view of Bloemenweg which - in contrast with the North Caves, with their very chaotic layout - demonstrates an extremely well-structured plan.

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Medallion This sculpture - created by J. Sondijker - was originally situated elsewhere in this tunnel network, along with many other drawings and sculptures. That section was known as the ‘Museum’ and was cut open by the cement industry. It is now no longer accessible, and the many artworks are disintegrating. >

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This medallion of ‘Maastricht Vooruit’ - the touristic association of the time - dating from 1899 was detached at the back, cut into blocks, moved here, and reassembled.

At the centre we see the Angel of Maastricht holding the city’s coat of arms: a five-pointed white star on a red background. To the right of the angel we see the St. Servaas bridge, the oldest bridge in the Netherlands. A bridge has existed on this site since the Roman era, and until well into the 19th century the St. Servaas bridge was the northernmost permanent crossing point on the Meuse. Half hidden behind the central figure, we can see the Basilica of St. Servatius (St. Servaas). To the far right we see St John’s Church (Sint Janskerk). This gothic church on the Vrijthof square can be recognized by its tall red tower, dating from the mid-15th century. >

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This tower was built using limestone from the Sint Pietersberg hill.

As the tallest tower in Maastricht, it is also battered by the most wind and rain. In order to make the stone extra resistant to the onslaught of the weather, the story goes that it was coated with ox blood in the Middle Ages. Every time this was done, 300 oxen had to be slaughtered. These days, a special paint is used. Every so often, the tower is restored where necessary and repainted.

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Crucifix MENU

This crucifix dates from the early 20th century and - like many drawings in these tunnels - was produced by Messrs Van der Veur and Simays. This larger-than-life crucifix is also jokingly called ‘Jesus with the short legs’. You can see that he has short legs and very long arms. The reason for this is that the artists would first produce a drawing on the wall before starting to carve. At that time, the standard practice was to use an oil lamp to project the shadow of a model onto the wall and to use this as a basis for the artwork. As the light source was usually positioned on the ground behind the model - in this case a person with raised arms - and the effect of this angle was that the silhouette was out of proportion. Colour has been used here, but it is not paint. To ensure that the colours used in the artwork remained on the wall, pure pigments have been used. >

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As such pigments are very expensive, charcoal has been chosen for most of the other works. The text above the figure of Jesus - I.N.R.I. - stands for the Latin ‘Iesus Nazarenus Rex Iudaeorum’ (Jesus of Nazareth, King of the Jews).

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Advertisements MENU

Circa 1900, when tourism slowly started to grow, it was generally only the wealthier people who were able to take a holiday. Those who were also able to travel were truly wealthy.

Several companies realized that many visitors came here to the caves and tunnels and - in consultation with the cave owners, and sometimes perhaps even at their request - decided to ‘decorate’ the walls with advertisements. >

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There are advertisements for local hotels and artisans, but also for large-scale nationally and today even internationally well-known companies such as ‘Bols’ (Dutch ‘jenever’ gin), ‘Alpha’ (margarine), and ‘Van Houten’ (cocoa). >

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The latter two are represented by large illustrations in colour. The imposing Van Houten advert - a few metres tall, depicting a boy shouting - is still very impressive. >

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The unique thing about these advertisements is that they are older than the advertisements painted onto the side façades of houses above ground at a later date.

These were in turn later superseded by the enamel boards and later still by radio and television commercials.

These cave illustrations were therefore the first advertisements aside from the actual packaging of the products.

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The Muses MENU

The ‘Salon der Muzen’ (the Salon of the Muses) was created here in the early 1900s by J. Sondijker, the third artist to have produced various works here alongside Van der Veur and Simays.

There seems to be no relevance to the underground situation, and this artwork was therefore probably created here purely for the sake of tourism.

Particularly when viewed by the light of a single oil lamp or carbide lamp, it must have made a big impression on the visitors. In particular, the details that we see in the hair and the lace collar of Kalliope (Calliope) bear witness to the great skill of the artist. The figures represent the nine daughters of Zeus, each representing the various arts and sciences as their patroness. >

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Walking close to the wall with the four ladies from right to left, keeping your eye on the trumpet held by Klio (Clio), the instrument appears to gradually get longer.

The effect can be easily explained by the slanting angle of the wall, but it’s a very intriguing illusion for most children.

The ‘block breaker’

The Romans started quarrying and using this limestone around 2000 years ago in order to treat the land with marl and for use as building stone. However, they did not quarry it by means of tunnels. They used open quarries cut into the side of the hill.

The creation of the tunnels began in the first half of the 13th century, when the city walls and the large churches were built. >

Building stone has been quarried here over a period of 700 years, with varying degrees of intensity. This ultimately resulted in a network of around 22,000 tunnels with a total length of around 230 kilometres. As a result of cave-ins and industrial quarrying on the surface (ENCI), a large proportion has disappeared.

The ‘block breakers’ who worked here centuries ago were generally farmers who owned land on top of the hill. Everything beneath their land was also their property. In contrast with the North Caves, in which the farmers quarried the rock beneath their land themselves, the quarrying of these tunnels was mainly contracted to professional block breakers, the best known of whom in the 16th century was Pieter Stas. This is clear from the many inscriptions that he left in these tunnels. >

These professional marl workers were able to work in a much more structured manner, more economically, and in particular more safely. With marl of this quality, they knew that they had to work on a 1:1 ratio. That meant that for every tunnel cut away, a pillar of the same dimensions had to be left standing to prevent the roof from falling in. The ‘healthy width’ of a tunnel is 4 metres.

Working long days in the poor light of a single oil lamp, at a temperature of 52 °F and in 98% humidity is of course very unhealthy. These days we know that a lack of daylight makes people susceptible to a depressive state of mind. The rheumatic and asthmatic conditions that were seen in so many of these people wouldn’t have improved their enjoyment of life much. In addition, they were very poorly paid. >

Ultimately, the first half of the 20th century brought an end to the underground quarrying of stone in the Sint Pietersberg hill. The useable layers of stone were as good as exhausted, and the cement industry - in the form of ENCI - began quarrying the hill from the surface in 1926, for instance by blowing up parts of it using dynamite and turning the loose limestone into Portland cement in its huge kilns.

Flint

Throughout the tunnel network, you can see a layer of a darker type of stone, running as a horizontal line through the hill. This is flint, one of the hardest types of stone in existence.

When the marl workers hit this layer with their simple saws and chisels, the flint simply broke their tools. This layer was also referred to as the ‘vloek’ (cursing) layer…

They were able to avoid the first layer because they found they could cut out good stone for about 1.5 to 2 metres below it. >

They then stopped cutting downwards because they knew that ‘our’ flint layer was the 23rd from the bottom. This - added to the fact that those layers got closer together the deeper they went - meant that digging deeper would result in more broken tools than useable blocks of marl. In contrast with the North Caves, the flint layer here lies lower, deeper below the surface, so the tunnels could be dug deeper.

Contrary to what you may have heard, striking two pieces of flint together won’t produce sparks or fire. In the Stone Age, when flint was used to make arrowheads, axes, and scrapers, people lit fires through friction which created heat. Flint was not used to light fires until the Iron Age.To create sparks, the flint needed to be struck with a piece of iron.

Scientists have not yet reached a universally accepted conclusion on how flint is formed.

Bats

The Sint Pietersberg hill, owned by the Vereniging Natuurmonumenten (Society for preservation of nature monuments in the Netherlands) since 1995, is also a well-known bat reserve. In the winter months, when temperatures outdoors drop below freezing and there are no flies or other insects to eat, the bats find shelter in the caves. Of the 19 species of bat known to live in the Netherlands, 15 spend the winter in these tunnels, seven of which are on the ‘Red List’ of threatened species. >

They crawl into the smallest holes and gaps, or hang upside-down high up on the walls to hibernate.

Their body temperature drops to 1 °C above the ambient temperature, and their heart rate shows to just two beats per 15 minutes. They are not bothered by light or noise, but warmth - even just the warmth of a torch - disturbs the hibernation of these mammals. Waking up costs them two weeks of sleep energy, so if they wake up too frequently, they won’t survive the winter.

The smallest species hibernating in these caves and tunnels is the Pipistrelle bat (Pipistrellus), so small it would fit inside a matchbox. It weighs about the same as a sugar lump. The largest species are the Greater mouse-eared bat and the Pond bat, which are said to be the size of a woman’s hand. >

The bats are counted every year, and that’s how we know that more than a thousand bats spend the winter in this network of caves and tunnels alone.

In the spring, when the outdoor temperature starts to rise, the scrawny, hungry bats fly out again and spend the summer in trees, church towers, or under roof tiles, some flying as far as 300 km away.

There, they feast on insects to gain weight and strength, and to build up a good layer of fat to see them through the next winter.

More MENU information

We have come to the end of this guided tour through the Zonneberg Caves. We hope you enjoyed your walk in this authentic part of the city of Maastricht. We would like to hear your opinion on this guided tour. To do so, please go to the Tripadvisor website – Grotten Zonneberg

For information on other locations of Maastricht Underground, go to www.maastrichtunderground.nl or ask your guide.

For further information on Maastricht and how you can make your stay extra special, surf to www.visitmaastricht.nl or see our colleagues at the Tourist Information Office, Kleine Staat 1, Maastricht. >

More information about St Pietersberg and its natural environment: www.natuurmonumenten.nl

More information about geology, the cretaceous period and fossils visit the Maastricht Natural History Museum, De Bosquetplein 7, Maastricht: www.nhmmaastricht.nl

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