 They are located on the slopes of mountains and are thus higher in elevation than their counterparts.It is believed, but not proved, that the Ganghwa dolmen are the earliest Korean ones made, because the designs of the dolmen in Bugeun-ri and Gocheon-ri are resemble those in Ganghwa.Dangun, the founder of Gojoseon, is said to have made an altar on top of Mani-san and offered sacrifices to his ancestors.