Two different stories from two different cultures to make something new for a third.
There was a celtic saint who died, but instead of being buried his body was laid to rest on the back of a wagon and hauled off by an oxen to travel the wild. It met a woman who cut off the oxen's horn, then smashed the dead saint's head in with the horn.
When the first viking family arrived at the shores of Iceland, the head of the family tossed over a pair wooden pillars carved with his gods. He found a safe harbour for the winter, but when the logs were found washed ashore he packed up his family and relocated to the harbour where they lay. This is now Reykjavik.
The wandergrave is a large, crablike machine golem made of thaumaturgium and necromantica. It is fuelled by the enzymes of decay. When a person of great import - typically a great saint or ruler - dies, their body is laid to rest upon it, and as it deteriorates the natural excretions run down into the engine, activating it and sending it forth on its journey into the wilderness.
As the rot sets in the wandergrave picks up considerable speed following a haphazard course and not unlike the juggernauts of farthest barbarica it will walk over or smash through any object placed before it. The wandergrave will continue until only desiccated bones remain, a matter of weeks in warmer climes, but of months or even years as the machine nears the poles.
At that point, where the last drop has been drained from the dead, the wandergrave comes to a standstill and collapses, forming a new sacred site and destination for the faithful. Aware of the pilgrims such holy locations attract, nearby merchants will often set up around the tomb, and as their needs must also be met, soon others gathers around the resting place of the dead and civilization rises from their grave.
