Simplify the following text for a Grade 7 native English-speaking person.
Original: The Middle Neolithic ( c. 3300 BC -- c. 2900 BC ) saw the development of cursus monuments close to earlier barrows and the growth and abandonment of causewayed enclosures as well as the building of impressive chamber tombs such as the Maeshowe types .
Simplified: The Middle Neolithic ( c. 3300 BC-c . 2900 BC ) saw the development of cursus monuments close to earlier barrows .