Maastricht possesses a subterranean network of mining galleries that extends under the Hoge Fronten, among other things.
Counter-mines were generally constructed in high ground, where the defenses had dry moats. In Maastricht, however, corridor systems were also found under lower ground, namely in the north of the Fortress and in Wyck (even though they were less extensive than those of the higher Fronten and it sometimes happened that certain galleries were flooded). The most forward mining galleries were usually under glacis and covered roads; the more rearward fortifications were usually partly mined.
Mining galleries were an indispensable element of the defense as, from the 16th century on, the enemy made use of subterranean gunpowder mines to breach the fortification belt. During the siege of 1579, mining galleries appear to have been present under certain sections of the covered road. They were constructed on Tapijn's orders and were equipped with mining chambers. Jump charges were used, for example, to destroy a Spanish trench outside the Tongerspoort. However, the engineer Plato's approach mine against the raveline was not detected in time, so the Spaniards managed to send a portion of the defense work flying.
The outworks constructed in the Tongersepoort-Boschpoort sector between 1632 and about 1648 were equipped with semi-permanent mine galleries, some of which were preserved until the 18th century. After the peace of Munster, these mines collapsed for lack of maintenance, until in 1672 a portion of the counter mines were restored to good condition. In 1673, the French restored the destroyed mine galleries in masonry. When the masonry gallery made its appearance in Maastricht, amorces, upright openings/niches in the sides of galleries, were made. In wartime, new transverse corridors, made of wood, could be built from such a niche.
The construction of countermines enabled one to detect the enemy's underground approach in time, destroy his positions, defuse his explosive charges, blow up abandoned fortifications and prevent a storming of breaches. This underground network remained intact. In addition to examples from 1690, 1747 and 1755 and 1759, the underground defense system mainly includes the mine systems constructed between 1770 and 1785 exclusively in masonry - marlstone walls and brick barrel vaults - which were built according to Du Moulin's guidelines and show a high degree of perfection due to their generous dimensions.
During the period of King William 1, a number of separate mining systems were also connected. In fact, this involved connecting the corners under the salient of the lunettes. This secret maze with its round domed chapels, its wide caponnieres , stairs, powder chambers and countless corridors represented a deadly danger to the enemy above and below ground. As soon as the approach of enemy miners was detected in the écoutes (listening corridors), the defenders dug a corridor from one of the many recesses in the gallery walls to the signaled point and attempted to detonate a bursting charge there.
If miners or commandos of the enemy penetrated a mine system, they found their way blocked by numerous doors, behind which were light mines hidden in zinc pits, which the vault could bring down on the intruders. Today, the underground labyrinth of about 12 km is a unique monument of defensive art.
During the Second World War, part of the counter-mine system was a shelter. The entrance at Borgesiusplantsoen in the Blue Village neighborhood is an example. Also on the Elisabeth Stroevenlaan, Aert van Trichtweg, ........
For example, the entrance to Bastion Maria was located in the garage of the former dairy factory Sint-Servatius on Statensingel nr.138.
In the inner city, cellars were connected at that time.