Why were the megalithic tombs built?

The construction of megalithic tombs was a huge effort. Up to 25,000 of them were built within a few hundred years. It has been estimated that the building of a megalithic tomb on average took 10,000 working hours. But why were such great resources invested in the construction and handling of granite blocks weighing up to 20 tons? One of the purposes of the work was to construct lasting monuments for deceased ancestors. The Neolithic burial monuments show that there was a connection between the world of the living and the world of the dead. In the world of the living the memory of the dead was crucial. That memory could be kept alive by building these enduring monuments. The monuments could presumably also mark territories – those who had built the monuments had the right to the land. Finally the actual construction process could also be important to the community. Gathering so many people and so much work together could strengthen the solidarity of the group.