Details such as accidents, occupations and prayer requests have survived, thanks to the extremely weather-resistant material of which the crosses are made.
Their geographic distribution is centred on the basalt quarries of Mayen and Mendig, and covers an area with a radius of approximately 30 kilometres between the Rhine, Ahr and Moselle rivers.
In the Early and High Middle Ages crosses were understood to provide protection from lightning, hail and other natural catastrophes.
The photograph shows an example of maximum economy in inscription writing e.g. MARIA House marks are signs and ownership symbols of the clans or noble families.
The rock is relatively easy to work thanks to its coarse pores, but so weather-resistant that it survives for centuries without being significantly affected.