A big dolmen with four petroglyphs that portray men with tridents and a wheel with spokes has been found at Kollur, near Tirukoilur, 35 km from Villupuram in Tamil Nadu. This is the second time that a dolmen with petroglyphs has been found in Tamil Nadu. The earlier discovery in the Nilgiris district was also made by Mr. Gandhirajan. But it was a circular dolmen.