Bronze became more common, hence the period 1700-500 BC became the Bronze Age and flint ceased to be used for tools. Large round mounds were used for burial, and more than 200 of these have been found on Møn. Each mound covered a single grave, containing a coffin made from a single split and hollowed oak tree. From 1000-500 BC, graves became smaller and cremation began to be practiced. Graves were encircled by a ring of stones. Fewer items were buried with the dead, as a result of changes in society which made grave robbing more likely.