The grave from Mammen can be dated to the winter of 970/971 AD. The precision of the dating is due to the preserved wood in the burial chamber. This wood’s felling date can be established with the help of so-called dendrochronology – known more popularly as “tree-ring dating”. In dendrochronology the width of year rings is measured in a given piece of wood. Next the width of the year rings in that piece of wood is compared with the width of year rings in a piece of wood of which the age is known. In this way the exact felling year can be determined. However, it presupposes that the outer year rings have not been chopped away. Furthermore, certain conditions relating to the species of tree and growth environment need also to be fulfilled.
The wood samples, which provide the basis of the dendrochronological dating of the grave from Mammen, were found in 1986. In this year the chamber was uncovered again by archaeological excavation.