Thanks to Christiansø’s geographic location, the fortress played a major role in two important conflicts in European history. The first was the Great Northern War (1700-1721), in which Denmark participated from 1709 to 1720. With Christiansø’s natural location between Sweden and Swedish Pomerania, the fortress served for extended periods as a base for a Danish blockade of the waters between mainland Sweden and its northern German possessions. This blockade was carried out by, among others, famed naval hero Peter Wessel Tordenskiold, popularly called Tordenskjold (literally Thunder Shield), who used Christiansø as a naval outpost. Under the guidance of Tordenskiold, the harbour was improved and a series of mooring rings were pounded into the rocks.
From Christiansø, Danish cruisers kept a sharp eye on the Swedish naval base, Karlskrona. A key reason why Christiansø was particularly well-suited for these tasks was that the fortress harbour rarely froze over in winter. This made it possible for smaller warships and cruisers to spend the winter at Christiansø.
The fortress was also used as base for privateers. One night, the island itself was invaded by Swedish privateers, who managed to set fire to a couple of ships in the fortress harbour before being killed.
Swedish privateers during the Great Northern War
During the Great Northern War in 1700-1721, Denmark was at war several times with its arch-enemy Sweden. In the past, when states conducted naval warfare, it was common to engage privateers. These civilian mariners were granted permission to arm their ships with weapons and cannons and embark on raids against enemy trade ships – basically it was state-sponsored piracy.
In the year 1718, Christiansø was visited one night by 24 Swedish privateers. They went ashore on these rocks and managed to sneak down and burn four ships in the fortress harbour. Christiansø’s soldiers were quickly mobilised, and the privateers were hunted down and defeated. Only the coxswain survived by hiding out among the rocks. On the Swedish privateer ship, the fortress soldiers found many valuable gold and silver items.
Christiansø lost only one man, while two were wounded. One of the injured soldiers was struck across the mouth by a sword and slit from ear to ear. They patched him up nicely, but for the remainder of his life, he had trouble speaking due to damage to his jawbone.
At the spot where the privateers went ashore, you can see a rock called Tyveskær (literally Thieves’ Rock), as a memorial to that dramatic night.