Assault on Copenhagen Day in Denmark Date in the current year: February 11, 2024

The assault on Copenhagen was a major battle during the Second Northern War fought between Sweden and its adversaries the Polish-Lithuanian Commonwealth, Denmark-Norway, the Tsardom of Russia, Brandenburg-Prussia, Habsburg Monarchy, and the Dutch Republic.

During the Second Northern War, Sweden and Denmark-Norway were engaged in two military conflicts known as the Dano-Swedish Wars. The first Dano-Swedish war ended in a crushing defeat of Denmark and the signing of the Treaty of Roskilde which forced Denmark-Norway to cede a third of its territory.

Several months later, King Charles X of Sweden decided to return to Denmark and vanquish it as a sovereign state, using Denmark’s failure to fulfill some provisions of the Treaty of Roskilde as a pretext to attack.

On August 6, 1658, the Swedish fleet embarked to the shores of Denmark. Five days later, it reached Valby hill (current day Frederiksberg). Since King Frederick III of Denmark expected the Swedes’ arrival, he had already ordered to burn every building outside the city walls, leaving about a third of the city’s population homeless, and closed the city gates.

Choosing between an assault and a siege, the Swedish king ultimately opted for the latter, hoping that starvation will make the Danes open the city gates. However, Copenhagen was well-prepared for the siege and didn’t give up despite daily artillery attacks. In November 1658, the Dutch fleet defeated the Swedes in the Battle of the Sound, ending the naval blockade of Copenhagen.

After the defeat, Charles X once again faced a choice: either to sue for peace or try to launch an all-out attack on the city, hoping to conquer it. Since the conditions of a new peace treaty would have been worse than the Treaty of Roskilde, the king decided to attack. The assault was planned meticulously, but the Danes knew all its details thanks to a number of spies and deserters.

For two nights in a row, the Swedish forces carried out diversionary attacks, which were repulsed by the Danes. To render the Swedish assault bridges useless, the Danes then broke the ice on the moats and the beaches.

At midnight on February 11, 1659, King Charles X ordered to commence the main attack. He led the main spearhead of the forces that attacked Copenhagen from the south. They quickly breached the outer palisades, but the chopped-up ice prevented them from advancing further. Eventually, the Swedes brought longer bridges and continued the attack toward the city walls, but in the end, the Danes threw the attackers back. Supporting attacks also failed, and around six in the morning, the Swedish king ordered a retreat.

The Swedes suffered heavy losses in the battle; 600 bodies were counted before the walls, and many more soldiers had drowned in the moats, whereas the Danes had lost only 14 people. The successful defense of Copenhagen was an important victory of the Danes, and its anniversary is now celebrated every year with a flag hoisting ceremony.