Nadukkallu or menhir is a Stone Age monument which was later known in the names pulachikkallu, masathikkallu or veerakallu. These are single rock slabs installed atop a burial site. The nadukallu is mentioned in ancient texts ‘Purananooru,’ ‘Akananooru,’ ‘Malaipadukadam’ and ‘Tolkappiam.’
Inscriptions of 10 and 11 centuries too have references on nadukkallu. Nadukallus inscribed with the name of the dead were installed at the burial sites of heroic warriors.
There was a practice in some regions to ‘offer’ alcohol to the nadukkallu to appease the "soul" of the deceased. According to the ancient text "Purananooru" penned by Mankudi Kizhar "nothing is worshipped except the nadukkallu".
Another custom was to bathe and offer bali (a Hindu ritual to propitiate the departed souls) to the structure in front of a ghee lamp.