Chambered long barrows, also known as megalithic long barrows or chambered tombs, were a style of monument constructed across Western Europe in the fifth and fourth millennia BCE, during the Early Neolithic period. Typically constructed from earth and stone, they represent the oldest widespread tradition of stone construction in the world. Around 40,000 chambered long barrows survive today. Many have been excavated by archaeologists, from whom our knowledge about them derives.