Simplify the following text for a Grade 9 native English-speaking person.
Original: The construction of the earliest earthwork sites in Britain began during the early Neolithic ( c. 4400 BC -- 3300 BC ) in the form of long barrows used for communal burial and the first causewayed enclosures , sites which have parallels on the continent .
Simplified: The construction of the earliest earthwork sites in Britain began during the early Neolithic ( c. 4400 BC - 3300 BC ) in the form of long barrows used for communal burial .