What is Passage grave?

A passage grave or passage tomb consists of one or more burial chambers covered in earth or with stone, and having a narrow access passage made of large stones. These structures usually date from the Neolithic Age, and are found largely in Western Europe. When covered in earth, a passage grave is a type of burial mound which are found in various forms all over the world. When a passage grave is covered in stone, it is a type of cairn.