[1] The successful defence of Copenhagen by the Dano-Dutch forces is not attributed by historians to their combined militaristic merits nor to the endurance of the city under siege.

Instead, the outcome of the siege and the subsequent battle are attributed to the poor planning and rash actions taken by King Charles X Gustav of Sweden, who ultimately sent his forces to be cannon fodder.

King Frederick III of Denmark chose to hold his ground and remain, reportedly stating that he would "die in his nest" (Danish: dø i sin rede).

[6][7] On the evening of 11 August Charles X and his forces reached Valby hill (current day Frederiksberg) from where they could overlook the Danish capital.

The city also had a sizeable reserve of defensive materiel: 50 tonnes (110,000 lb) of lead, 4,000 muskets, and a staggering 810 kilometres (500 mi) of slow match.

[9] The Swedish fired over 200 heated shot a day into the city, and several large howitzers were brought to bombard the Danish capital, including the 300-pounder "Eric Hansson", earlier used in the siege of Kraków.

On August 23, 1658, almost 3,000 students, sailors and soldiers staged a surprise sortie through a hidden passage in the wall, destroying fortifications under construction and capturing three cannons.

Before the trench was complete, however, a Dutch relief fleet arrived under Lieutenant-Admiral Jacob van Wassenaer Obdam leading to the Battle of the Sound on 29 October 1658.

[5] Danish spies learned that the attack was to take place on the night of 10 February, and warned the Copenhageners who planned their defences and stockpiled weapons and ammunition.

[13] The walls of Copenhagen bristled with about 300 pieces of cannon, mortars and other artillery, while a diverse mixture of weapons, ranging from muskets and arquebuses to morningstars, scythes, boiling water and tar had been readied for action.

[citation needed]Danish spies reported that the Swedish army had moved from their camp, Carlstad, at Brønshøj and had taken up positions behind Valby Hill.

The Swedes, intending to make a surprise attack, had dressed in white clothing to blend in with the snow and fog as they advanced across the frozen strait towards Copenhagen.

[13] The main assaults were made against Christianshavn and Vestervold, but the chopped-up ice and the massed weaponry on the wall caused the Swedish forces to take a horrific number of casualties.

[1] The Dutch in the spring of 1659 sent a second fleet and army under Vice-Admiral De Ruyter to further reinforce the city and cut the Swedish supply lines so that the siege would have to be lifted altogether.

[6] Although the Dano-Dutch victory in Copenhagen forced Charles X to abandon ambitions of a complete conquest of Denmark, it was not the impetuous for peace negotiations.

[3][4][13][16] Negotiations were opened and the Treaty of Copenhagen was signed on 27 May 1660, marking the conclusion of the Second Northern War between Sweden and the alliance of Denmark-Norway and the Polish–Lithuanian Commonwealth.

[2] Taksigelsesfesten was celebrated annually until 1766, when it was abolished following the marriage of the King's daughter, Sophia Magdalena, to the crown prince of Sweden, Gustav III.