T he Petrovaradin Fortress is an old medieval Hungarian fortress built in the 13th century. In 1526 it was attacked by the Turks, and after a two-week siege, the Turkish army resorted to underground warfare. The fortress remained in Turkish hands until 1687 when it was won by Austria during the Grand Vienna War. It was lost again, and won again by the Austrians in 1692, who embarked on a rebuilding and strengthening program until 1727 that developed into the fortress we see today.
The Austrians expanded the underground tunnel network, the bastions of Hornverk and Wasserstadt, as well as a bridgehead and small fort on an island in the Danube. On some older maps you can see an extensive system of bastions in front of Hornverk, labeled "Crownwerk." The foundation was constructed for this fortification, but because of an earthquake in 1722, it was never completed. The earthworks were destroyed during a later expansion of the fortress after 1753.
In 1762, the Austrians lost Schweidnitz Fortress to the Prussian army, in part, because they were not able to fight well underground. The Austrians learned from this failure, and Austrian engineer Alrech Heinrich Schroder (Major commandant of Mineurs Corps) was brought in to develop a way to protect Petrovaradin Fortress’ network of tunnels in the event of another war with the Ottoman Empire. By 1764 he had put together a plan for more tunnels beneath Hornverk. Four hundred people worked from 1764 to 1776 on the project. Emperor Joseph II, himself, visited the tunnels in 1768, 1783, 1786, and 1788. During his first visit, he was so impressed during the military inspection that he promoted Schroder, and ordered the building to continue at an accelerated rate. To this day, there is a well in the fourth level named after Joseph II.
When the tunnel system was completed, Petrovaradin’s defenses were second only to the Antwerp fortress. The upper fortress has 16,000 meters (9.94 miles) of tunnels. These proved useful in 1813 when Napoleon attacked the Russian Empire; the Austrian crown jewels were hidden in the tunnels of the upper fortress.
In a time of siege, Petrovaradin fortress can accommodate 10,000 people, and 4,000 cent of powder. The underground system can handle an additional 6,000 people, but the powder magazines can only hold 2,000 cent of powder, and not enough food for everyone.
Powder Magazines:
One in upper fortress
One in Hornverk
Three in downtown
One in bridgehead
One near Kamenitz village
Three on the left side of the Danube
In times of war, Petrovaradin standing garrisons is:
General staff: 64
Infantry: 8,134
Cavalry: 120
Artilleryman: 863
Chambermaid's: 21
Engineer's and Miners: 93
Proviant service: 89
Total: 9384
Tunnels under Hornverk:
Each gallery has a sign of rough-hewn marble (some up to 51cm square) which lists the level number (I through IV), the tunnel number (1 through about 527), an arrow indicating the direction in which the tunnel continues, and the name of the tunnel (i.e. “Prinz Eugen Mine,” or “Karls Mine.”) Some of the galleries include:
The Communications Galleries (Kom Gall)
The Eavesdropping Galleries or Listener's galleries (sometimes called "H.G." which is short for "Horch Gall." Horchen means “eavesdrop”)
The End Gallery (End Gall)
The Attachment galleries (Verbindungs Gall) - Linking various tunnels
The Entrance (Abgang) and Exit (Ausgang) Galleries between levels
The Exit to Surface (like "Ausgang to Ludwigst retr.")
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