The Nagarathars migrated towards Pandya kingdom. The reason is that one of the Chola kings fell in love with one of the nagarthar girls, but the King refused to marry her. The nagrathars requested the King to marry her, but the king was very stubborn.Therefore the whole women community gave up their life and the men moved to the Pandya kingdom. The Pandian welcomed the Nagarthars and asked them where they wanted to live in his land. The nagrathars opted for the Chettinad Area. The Pandian wanted the community to grow and therefore he requested the nagrathars to marry again. Therefore they married the girls from the Saiva Vellalar community from Tirunelveli area. May be that is the reason they still have the practice of addressing the dad as Appachi and mom as Aatha and the granny as Appatha.