After the lid had been placed on the oak coffin containing the deceased, the burial mound was built. The mound was constructed of turf laid with the grassy side down. Once the mound was finished a wall of stones was erected around its base. Inside the waterlogged mound a chemical process took place. After a while a ferrous layer was formed that sealed the core of the mound. In the wet and oxygen-poor environment there was no decomposition. The dead and their clothing have thus been preserved until today.