Barrows are burial mounds. Megaliths are made from huge slabs of stone. Sometimes they are tombs too. No one is sure what they were used for. 3000 years ago Homo erectus to Cro-Magnon man gather plant food and hunt with flint weapons.
Population grows and craft skills develop.
Bronze-making invented in SE Europe and Near East. Barrows and megaliths built. Use of iron spreads from Near East. Rise of Classical Greek civilization.