One of the densest manifestations of the megalithic phenomenon in Europe occurred in Portugal. In the north of the country there are more than 1000 late prehistoric barrows. They generally occur in clusters, forming a necropolis. The method of inhumation usually involves a dolmen. The tumuli, dated from c. 4450 to 1900 BC, are up to 3 metres high, with diameters from 6 to 30 metres. Most of them are mounds of earth and stones, but the more recent ones are composed largely or entirely of stones (cairns). In Portuguese, barrows are called "mamoas", from the Latin "mammulas", given to them by the Romans because of their shape, similar to the breast of a woman.