Dunshammar Blast Furnaces Blast
Dunshammar is one of the few places in all of Sweden where you can see Iron Age furnaces in their original setting. Beautifully situated on the eastern shore of Lake Åmänningen, these furnaces remain just as they were an astonishing 1,700 years ago! It’s a mind-bending experience to visit Dunshammar today and wonder how Iron Age people could construct furnaces that are still so well-preserved?
From the forest parking area, a picturesque woodland path leads 300 meters down toward the lake. Here, the Iron Age people dug their blast furnaces, named after the process of blowing air into the fire using bellows. This made the furnace hot enough to melt the ore and separate the iron from the slag. At this time, people hadn’t yet developed the technology to build tall furnaces; instead, they dug small pits in the ground, which were sealed with stones and clay.
Iron from rock hadn’t yet been discovered, so the ore was sourced from the lakebed. During summer, boats or rafts were used to retrieve the iron-rich sand from the bottom of the lake. In winter, holes were cut in the ice to access the lake ore. This lake ore, containing up to 60% iron oxide, lay as small lumps on the lakebed.
Over the centuries that Iron Age people lived here and produced iron, they occasionally discovered ways to make the production process easier and more efficient. They also learned to produce greater quantities of iron. Lake ore contained phosphorus, which made the iron hard and brittle. By roasting the ore—stacking layers of firewood and igniting them, then placing the ore on top of the blazing fire to drive off moisture and impurities before smelting—it became easier to forge.
Once the ore was roasted, the blast furnace was heated with charcoal, and the roasted ore was added. To reach the necessary temperature of approximately 1,100 degrees Celsius, workers pumped the bellows for an extended period, ensuring the fire grew hotter. After hours of pumping the bellows and adding more charcoal and roasted ore, the slag would settle at the bottom of the furnace. Over time, the iron would clump together and rest atop the slag.
Eventually, people discovered that the hotter the furnace, the harder the iron became, making it suitable for tools and weapons.
At Dunshammar, you can see not only the small dug-out blast furnaces but also a charcoal pit where the charcoal was made and several slag heaps—the heavy, rust-brown byproduct that melted before the iron during the smelting process.
There is also a small museum that illustrates the process in both text and images.
Facts
Unique Iron Age site with small dug-out blast furnaces and a small museum.
The site can be visited independently regardless of opening hours and is well-signposted.
The museum is open during the summer months.
Archaeological excavations were conducted on the site in 1969–70 and 1985. The furnaces have been dated using the C14 method to the 3rd–8th centuries.
Archaeologists estimate that 6–7 tons of iron were produced here over the centuries.
The gravel road to the parking area is narrow.
Eight kilometers south, around Västervåla Church and Virsbo, Iron Age graves have been discovered.
