In the summer of 1657 Danish/Norwegian King Frederik III thought himself clever when he declared war on Sweden - while they were occupied with fighting in Poland - and send troops into Sweden.
Very unfortunately for Denmark the Swedish King Karl X Gustav immediately ended his campaign in Poland and marched west towards Jutland, which was taken in the fall of 1657. Since the Danish navy was stronger than the Swedish it didn't seem critical, but then it started to be a very harsh winter and the Belts froze over, keeping the Danish/Norwegian navy in ports.
The Swedes were able to cross the Little Belt and take Funen and then also cross the Great Belt landing on Zealand.

The Danes were forced to a very hard peace in Roskilde 1658 with the Danish loss of Scania, Halland, Blekinge, Hven and Bornholm and Norwegian loss of Båhuslen and Trondheim-len.
Then after the peace the Swedish King reconsidered; why shouldn't he end Denmark once and for all while his army still occupied all the Danish territories except Zealand? So Karl X Gustav broke the peace and send a force to siege Copenhagen.
The Danish/Norwegian King Frederik III was advised to flee to Norway, but he declared that he "would stay in his nest" bolstering the defenders moral. When the Swedes took Elsinore and Kronborg castle in September the Danes in Copenhagen were totally boxed in.
The Dutch had promised to help Denmark in case of an unprovoked attack and a Dutch navy was able to break through the Swedish naval siege and land 2000 marines to help with the defenses. The Dutch had supported the Swedes in war 1643-1645 against Denmark to avoid the Danish Sound Toll, but now it looked that by weakening Denmark, they had made it possible for a much more powerful country to emerge as controller of the Sound Toll.

The Swedish siege force were eventually a professional 9000 man strong against ~10.000 defenders. Besides the 2000 Dutch, you had a mix of Danish professional soldiers (3000 men), city militia (3500) and the rest other willing townspeople. The population of Copenhagen was 29.000 at the time.
When the Swedes attacked in Feb. 1659, Danish spies was aware of the three locations in time to inform the defenders, so they could put on a strong defense including ambushes. It was a disaster for the Swedes. The Swedes lost 532 dead and 894 wounded before the attack was called of, with only 12 Danes died (other sources say 17 Danes, so I guess that is wounded that died after the battle).
The first Swedish officer that managed to actually scale the Danish defenses was killed by Claus Ahlefeldt using his partizan.
This weapon thus received cult status, as Denmark was saved as a country (and Danes as a people, when you later see what happened in Scania, Halland and Blekinge).
The dual existence of Denmark/Norway and Sweden/Finland (critically on each side of Øresund so no one could control the strait and exact a Sound Toll) was especially of interest to Holland, England and Russia -> so this was the last time a united Scandinavia was close to form.

[ Linked Image ]
Source: http://upload.wikimedia.org/wikipedia/commons...rtical.jpg
The weapon is 265,5 cm long.

For bigger pictures:
Source: http://upload.wikimedia.org/wikipedia/commons...rtical.jpg
Source: http://upload.wikimedia.org/wikipedia/commons...agonal.jpg

Picture with darker background:

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Claus Ahlefeldt's partizan.
Source: http://samlinger.natmus.dk/DMR/168065

Here a later historical painting by Vilhelm Jacob Rosenstand (1889) of the overall commander Hans Schack (presumed) talking with Claus Ahlefeldt (presumed) with his partizan leading the Students of Copenhagen at the "Storm" (when the Swedes attacked).

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Source: https://s-media-cache-ak0.pinimg.com/736x/fa/26/7b/fa267bb667d0b44b1df61a6f6040efbb.jpg
His partizan is painted way to short, though.

The enrolled "Student Contingent" were apparently 266 men strong.

Other pictures of the "Storm" - first two historical paintings by Frederik Christian Lund:

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Source: http://www.2700-netavisen.dk/wp-content/uploa...enhavn.jpg
Frederik Christian Lund (1880).
From auction of painting that shows enlarged details: http://www.lauritz.com/en/auction/frederik-ch...2/?nBids=5

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Source: http://historiskerejser.dk/wp-content/uploads...enhavn.jpg
Frederik Christian Lund (1887)
Big size picture: http://www.danculture.dk/wp-content/uploads/2013/10/IMG_3260.jpg

The dutch painter Daniel Vertangen (1601-1683) provides a contemporary view (from outside the walls).

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Source: http://a.bimg.dk/node-images/376/620x/376239-dden-p-isen--.jpg

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I never knew that Ahlefeldt's partizan still exists today after his demise centuries ago. Where is it currently kept?

A fascinating bit of history - thanks Niels. There are clearly still huge chunks of European history which I know next to nothing about. Also nice to have an account of a partisan actually in use in hand-to-hand combat - I've long been partial to partisans, but most secondary/modern sources which I had read suggested that they were usually more symbols of command or ceremonial in nature, while downplaying their effectiveness as weapons. This one clearly shows that a weapon can be both ornate and functional. Do you know if the inlayed (gold?) designs on the blade are an original part of the weapon, or a later embellishment (after it had attained its historical status)?

Interesting background information about Claus Ahlefeldt.... and it explains a lot about a few things that puzzled me initially:

1. How people even knew the name of the guy who killed the first Swedish officer into the breach;

2. Why he did it with such a fancy weapon; and

3. Why the feat has made him such a cult hero to this day.

I had made some incorrect assumptions about the gentleman based on that first painting of him at the siege, and I suspect others may have as well: since the painting shows him at the head of a company of university student volunteers, I had assumed he was a relatively unimportant young college student himself at the time.

That he was actually 45 years old, was born into a great noble family and had married into the royal family, had served as an officer under Wallenstein during the 30 Years War, and now held general officer rank -- that puts a rather different picture on his actions.

Freshly minted junior officers are EXPECTED to stand at the head of their company as it repulses the enemy's Forlorn Hope in the breach; commanding generals are EXPECTED to leave those sort of heroics to the idiot young ensigns and 2nd lieutenants while they stand back, view the overall scene, and direct some captains on where to lead the reserve companies to plug impending gaps. The commanding general is EXPECTED to lean gracefully on his fancy partizan while issuing these orders; he doesn't get BLOOD on the wretched thing... No wonder this particular feat of arms was so notable...

Painting of Claus Ahlefeldt:

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Source: http://www.alt-bramstedt.de/Inhalt/Schloss_Gu...age045.jpg

Painting by unknown artist and date, that apparently was in the hands of the Ahlefeldt-Laurvig line at Tranekær (Counts of Langeland), but was sold at an auction around 1800 to Austria. The family later tried in vain to by it back, but was at least allowed to make a copy, which is at Tranekær today. Original is in private ownership in Salzburg.