At places where barrows have been constructed, they are usually found in groups (10 to 100 together), often forming several clearly distinct lines going from the west to the east. Only a few of them have been studied scientifically so far; in them, both burials by fire (with burnt ashes) and unburned skeletons have been found, even on the same site. It seems that builders of the barrows have at some time switched from burials by fire to burying of unburned corpses; the reason for such change is unknown. The barrows date too far back in history (700 AD to 800 AD) to contain any Christian influences.As Czech barrows usually served for burials of poor villagers, only a few objects are found in them except for cheap pottery. Only one Slavic barrow is known to have contained gold.