Simplify the following text for a Grade 11 native English-speaking person.
Original: A dolmenâ '' also known as a portal tomb , portal grave , cromlech ( Welsh ) , anta ( Portuguese and Galician ) , HÃ 1\/4 nengrab\/H Ã 1\/4 nenbett ( German ) , Adamra ( Abkhazian ) , Ispun ( Circassian ) , Hunebed ( Dutch ) , dÃ s ( Swedish ) , goindol ( Korean ) or quoitâ '' is a type of single-chamber megalithic tomb , usually consisting of three or more upright stones supporting a large flat horizontal capstone ( table ) .
Simplified: A dolmen ( also known as cromlech , anta , HÃ 1\/4 nengrab , Hunebed , quoit , and portal dolmen ) is a type of single-chamber megalithic tomb . It usually consists of three or more upright stones ( megaliths ) supporting a large flat horizontal capstone ( table ) .