The oldest tar pits in Sweden date from around 100AD to 400AD. The first were discovered in the early 2000s, and are found close to old settlements, suggesting that the tar was for coating houses and household items. It was made by stacking pine wood into conical pits a metre or two across, setting the wood on fire and covering it with turf and charcoal to encourage a slow combustion. In this way, the wood's resin would turn to tar and drip out of the cone's bottom into a buried container.