Jihlavasko Podzemi

These catacombs are the second longest in the Czech Republic after Znojmo Podzemi, they are situated directly beneath the old town and form a significant part of the town's ancient architecture. They cover an area of 50,000 sq. m. and they comprise of multiple-level catacombs which have been cut into the solid rock. They are found under almost all the houses in the centre of Jihlava, and they have been declared a municipal conservation area. The first level of the catacombs can be accessed from basements at about 2 to 4 metres below street level; the second level lies about 4 to 6 metres below street level. Under several houses, there even are third-level cellars situated 8 to 14 metres underground. The first-level corridors were built during the 14th century, the second and third-level corridors were added in the 16th century, and, finally, during the 17th century, some of the corridors were reinforced with brick foundations and the individual sections interconnected with a network of short corridors.

The underground passages are 0.8-2. m wide and 1.2-3.5m high. In the middle of each passage, there is a shallow gutter to drain all the water which is either collected from the walls or has trickled down from the surface. In former times water flowing under gravity through the walls was collected in small troughs dug in the deepest parts of the corridors and some of the water thus collected drained naturally into the ground or was used as drinking water. Air shafts going all the way up to the surface provide ventilation for the passages. Many of the passages have access to underground wells.

In addition to the main walking size passages, there was a network of tunnels measuring 0.6-0.7 metres in width and 1.0-1.7 metres in height, forming the town's sewage system. There are many places where these original sewer tunnels still serve this purpose to this day - reinforced and connected to a modern sewer system, of course.

Numerous theories have been postulated as to why these catacombs were excavated. For a long time, historians believed the galleries were ancient silver mines abandoned long ago. Others maintained that they were built for military purposes. Contemporary historians tend to believe that the main purpose of the passages was for storage, most likely for wine and pickles. Thanks to its position on an important crossing of ancient trade routes, Jihlava's prosperity did not diminish after the decline of silver mining, as the town began to rapidly develop both commerce and trading. Merchants and tradesmen needed to store their goods safely - and expanding their cellars was a logical thing to do, especially since there were many experienced miners in Jihlava to do the work.

At the beginning of the 18th century, the catacombs were no longer used as frequently and, towards the end of the century, several of the former storage corridors were converted into sewage tunnels. In the 19th century, during the installation of water mains and gas pipes, and the construction of new houses, many of the corridors were filled with debris. Thoughtless dumping of the debris often damaged the old drainage system, causing the corridors to get flooded with water. With much effort and hard labour, the original passages had to be restored to protect the foundations of the houses above from damage by underground water. The integrity of the catacombs was further affected after many of the owners built partitions between houses. During the German occupation, some of the underground passages were converted into air-raid shelters. In the first years after the war, there was little interest in the catacombs and it was not until 1957 that the first kilometre of passage was opened to the public.

During the sixties, nearly all of the corridors were reinforced with concrete, all of the debris was removed, and the medieval drain system restored. Due to these public works, the profile of some of the corridors had to be lowered, but the part which is open to the public was left in its original condition. In 1969, the catacombs were closed to the public, and were reopened in 1991. During work on the paving of the main town square and the streets around it, most of the ventilation shafts were blocked up, again, causing a considerable humidity, resulting in condensation underground. The temperature in the catacombs ranges between 8 and 12°C.

In 1978, a group of amateur speleologists discovered the so-called Shining Corridor. The walls of the corridor are covered with a milky coating which emits a greenish light after exposure to light. The vaulted passage lies about 11 metres under the street level; it is 2.1 metres wide and 2.9 metres high.

For a very long time, no one could find a reason for the shining corridor's fluorescence and many theories were aired for this phenomenon. According to one of them, the fluorescence results from the emission of phosphorus from the bones of the monks who had been buried in one of the corridors above it; according to another story, an unknown organic substance causes the radiation. Jihlavský Netopýr (Bat of Jihlava), a citizens association, called in specialists from the Mineralogy Department of the Faculty of Natural Sciences at the Charles University, Prague, to help resolve the mystery. Their analysis of samples revealed that it was a man-made substance with a long afterglow. The substance, containing zinc sulphite and barium, had been used in the mortar mixture which had been applied to the walls. Just what purpose the coating may have had, and whose idea it was, is no longer known. It is speculated that it might have been used as emergency lighting at the time when the catacombs were used as an air-raid shelter, or that some kind of illumination tests were performed there.

Text by Tony Oldham (2002). With kind permission.