Akershus Fortress: 700 Years Guarding the Oslofjord

Akershus Fortress is a medieval castle on a promontory above Oslo's inner harbour, begun by King Håkon V Magnusson around 1299 (Store norske leksikon dates the building work to roughly 1299–1304). It has been attacked repeatedly and never taken by storm. It changed hands once, on 9 April 1940, by surrender rather than assault, and came back under Norwegian control on 11 May 1945. The grounds are free and open all year; the museums inside charge admission.

Hanseatic cogs, Swedish men-of-war, a German invasion fleet and the white commuter ferries to Nesodden have all passed under these walls. If you have questions about the water the fortress looks out over, our frequently asked questions cover most of them.

Timeline: 1299 to 1945

Dates from Store norske leksikon and lokalhistoriewiki.no.

1299: the capital moves east

Håkon V Magnusson moved the seat of the Norwegian crown from Bergen to Oslo, part of a wider reorientation of the realm toward the east that Store norske leksikon traces through his reign. Bergen was the country's trading capital and increasingly the Hanseatic League's. Oslo was smaller, poorer and much closer to Sweden, which is where Håkon expected the next war.

The castle went up on the rocky point that pushes into the harbour. Bedrock drops steeply into the water on three sides, and any ship heading for the quays had to pass under the walls. What Håkon built was a garrison: thick stone, a keep, and storage enough to sit out a siege.

Five sieges in four hundred years

Lokalhistoriewiki lists attacks in 1308, 1449–1450, 1502, 1567 and 1716, none of which got through, and sums up the record in one line: the fortress has been attacked several times and never taken by storm. Store norske leksikon notes that as early as 1308 it could see off the Swedish duke Erik Magnusson.

The last attempt was the most serious. In 1716 Karl XII of Sweden took Christiania itself, but the fortress held, and the Swedish army pulled back at the end of April after 39 days (Store norske leksikon). Karl was killed two years later at Fredriksten, another Norwegian fortress, without ever taking this one (Store norske leksikon).

From castle to Renaissance residence

Gunpowder changed the arithmetic. Cannon could break stonework that had shrugged off battering rams for centuries, and across Europe military architects were rebuilding fortresses with low, angled bastions that absorbed shot and covered each other's flanks.

Akershus got that treatment under Christian IV, the Danish-Norwegian king who had the medieval castle reshaped into a Renaissance residence, tearing down a good deal of it and building new so the place could serve as a royal seat (Store norske leksikon). He rebuilt the city at the same time. After the fire of 1624 destroyed old Oslo, he laid out Christiania on a new grid directly beneath the fortress walls.

The bastions are what you see most clearly from a boat: angular grey walls pushing out from the promontory, each covering its neighbour, so an attacking fleet would have taken fire from more than one direction at once. Inside them, the halls were fitted out for court life. Akershus spent the next three centuries as garrison and seat of government at the same time.

9 April 1940

Germany invaded Norway before dawn. A naval task force came up the Oslofjord in darkness with orders to take the capital, arrest King Haakon VII and capture the government before it could leave. The lead ship was the heavy cruiser Blücher.

She never reached Oslo. Thirty kilometres south, in the Drøbak narrows, Colonel Birger Eriksen ordered the guns of Oscarsborg to fire without waiting for clearance from the high command. Two 28-centimetre Krupp shells hit the cruiser, then two torpedoes from a concealed shore battery struck below the waterline. Blücher burned for three hours and sank. Store norske leksikon puts the dead at 576 of the crew and around 400 of the embarked troops. English-language accounts differ sharply: the survey of the historiography ranges from Jürgen Rohwer's 320 dead to Henrik Lunde's 600 to 1,000, with Erich Gröner calling the figure unknown. The rest of the fleet turned back.

The delay gave the king and the government time to leave Oslo by train that morning. Roughly 49 tonnes of gold from Norges Bank, booked at 240 million 1940 kroner, went out by truck and eventually reached the Bank of England, the Federal Reserve in New York and the Bank of Canada (Store norske leksikon). Had the invasion fleet tied up at the quay on schedule, none of that would have got out.

Akershus fired nothing that morning. The fortress was surrendered without combat when the government evacuated. Its medieval and Renaissance defences were built against a different kind of attack, and the garrison was small.

The occupation years

The Germans ran Akershus as a barracks camp on Festningsplassen, a prison and an execution ground (Store norske leksikon). Norwegian resistance members were held inside walls built to keep enemies out.

Forty-two Norwegians were shot at the execution site, all of them in 1945. The first were hostages killed on 9 February in reprisal for the liquidation of the police general Karl Marthinsen (lokalhistoriewiki.no). The spot carries a memorial today. We pass those walls on every private cruise and I mention it every time, because I think you should know what happened there before you admire the architecture.

The Norwegian Resistance Museum occupies building 21 inside the fortress and is run by Forsvarshistorisk museum. It opens 10:00–17:00 daily from May to August and 10:00–16:00 from September to April. An adult ticket is 160 kroner, 110 for students and pensioners, 80 for children aged 6 to 17, and 400 for a family (prices checked July 2026). The exhibits are detailed and unflinching: names, dates, photographs. If you visit one museum in Oslo about the war, make it this one.

11 May 1945: the handover

German forces in Norway capitulated on 8 May. Three days later the ranking German officer at Akershus, Major Josef Nictherlein, formally handed the fortress to Terje Rollem of Milorg (lokalhistoriewiki.no).

Then the place did one more grim job. Norwegian collaborators were imprisoned, tried and executed inside the walls, Vidkun Quisling among them. He was shot at the western wall of the old powder magazine on 24 October 1945 (Store norske leksikon).

What you see from the water

From a boat, which is how we see it on every cruise, Akershus appears the way it was meant to: from below, at an angle that makes the scale obvious. The walls rise straight out of the waterline, their lower courses dark with age and tide. Medieval towers stand against the sky. The bastions push out in angles that still look modern.

The promontory is bedrock and the medieval builders used it. From the water you cannot tell where the cliff stops and the wall starts. There is a moment on every trip, right as we round the harbour bend, when guests stop talking and reach for their phones. It is a lot of stone.

At sunset the walls go amber, and at night floodlights pick out the ramparts. In winter, snow settles on the works and the whole thing looks borrowed from another century. The contrast is what most guests comment on: the glass towers of the Barcode district on one side, seven hundred years of masonry on the other.

Visiting Akershus today

The grounds are free and open all year. You can walk the ramparts, look out over the harbour and stand where sentries have stood since the 1300s. The view alone earns the walk: the Opera House across the water, the Aker Brygge waterfront, the fjord running south toward the islands.

Three things inside are worth the time. The castle is open for guided tours through the royal halls, the chapel where Norwegian kings are buried and the dungeons, which were still in use well into the twentieth century. The Resistance Museum covers the occupation. The Armed Forces Museum covers Norwegian military history more broadly. Half a day does all three, and most people underestimate the Resistance Museum and lose an hour in there.

The address is Akershus Festning, 0150 Oslo. The fortress is managed by Forsvarsbygg, the Norwegian Defence Estates Agency. Guided tours of the castle run mainly in summer, roughly May through September. The grounds are a short walk from Aker Brygge or the central railway station.

Opening hours, tour seasons and museum prices change from year to year. The museum prices above were checked against Forsvarshistorisk museum in July 2026; check Forsvarsbygg's Akershus page for current fortress hours before you go. Last reviewed: July 2026.

For the wider context around what you see at Akershus, the University of Oslo's Norgeshistorie is the most authoritative free resource on Norwegian history.

Seven hundred years of watching the fjord

Viking fleets passed this headland before the fortress existed. After them came Hanseatic merchants, Swedish armies and a German invasion fleet. Now, on a summer evening, a small boat carries seven people past the walls on the way out to the islands.

Akershus has outlived the medieval kingdom that built it and the union that rebuilt it. It is the first landmark our guests see leaving the harbour and the last one they see coming back.

Akershus has guarded this harbour since 1299. We pass the curtain wall on every south-bound trip, and you can pick out where the medieval stone ends and the 17th-century rebuild begins: the colour shifts from grey-brown to a paler grey. In seven hundred years nobody has taken it by storm.

Sources

• Store norske leksikon — Akershus slott og festning (construction 1299–1304, the 1308 attack, the 39-day siege in 1716, the Renaissance rebuild, German use of the fortress as barracks, prison and execution ground).
• Lokalhistoriewiki — Akershus festning (siege chronology; "never taken by storm"; 42 Norwegians executed in 1945, the first as hostages on 9 February; the handover on 11 May 1945).
• Store norske leksikon — Håkon 5. Magnusson (the king who moved the seat of the crown from Bergen to Oslo).
• Store norske leksikon — Christian 4. (the Renaissance rebuild and the founding of Christiania in 1624).
• Store norske leksikon — Karl 12. (the 1716 invasion of Norway and the siege of Fredriksten).
• Store norske leksikon — Blücher (the sinking on 9 April 1940; 576 crew and around 400 troops dead).
• Wikipedia — German cruiser Blücher (the competing casualty estimates from Rohwer, Lunde and Gröner).
• Store norske leksikon — Gulltransporten (roughly 49 tonnes of gold, booked at 240 million kroner, moved out of Norges Bank in 1940).
• Store norske leksikon — Vidkun Quisling (trial and execution at the fortress on 24 October 1945).
• Forsvarshistorisk museum — Norges Hjemmefrontmuseum (location in building 21, opening hours and ticket prices).
• Forsvarsbygg — Akershus festning (heritage management; visitor information).
• Norgeshistorie (Universitetet i Oslo) — 1940–1945: andre verdenskrig (occupation context).