Article by Pasupathi K Pillai
also see http://en.wikipedia.org/wiki/Ettuveetil_Pillamar

They were once princes in AD 1730, and loyal to the erstwhile Thiruvithangore Samasthanam Kerala Marthanda varma King. Later on these governors of the samasthanam went against their salt, revolted against the King Marthanda varma. Finally the King won, and the defeated 8 veetu pillais ran away from Trivandrum - Thiruvithangore saamsthanam to Srivaikundam and Tirunelveli. Some say the sister or princess of the 8 veetil pillaimar brothers loved the King Marthanda varma, which was not liked by the borthers, which created the rift between the Travancore Raja and the princes. Some other story says the 8 brothers tried to grab the Travancore rule. Anyhow, they all men from that 8 veetil pillai family were killed. Women and children sold to fishermen as slaves. So the rest escaped to Tamilandu to live in a fortified way, to safeguard the women. So they became the famous "Kottai Pillaimar" or the Sivagalai Pillaimar or the Sevagalai Pillaimar or the Sevalai Pillai. There is a research work on this Kottai Pillaimar - the Pillaimar who lived inside Forts. Even many descendents of these marthandavarma family live in and ariound the Tirunelveli District.

See more about this Topic in the following sites:
There is a book available in Amazon on them.
Boundary Walls: Caste and Women in a Tamil Community (Studies in Sociology and Social Anthropology)

A complete book on Marthandavarma by CV Raman Pillai on the net

http://www.changanachery.com/html/history.htm

http://www.hindu.com/

http://naturemagics.com

http://harringtonstore.com/marthandams/   

Karuvukarattil Pillaimar Arukuttattil Pillaimar
...those classified as Ettuveettil Pillaimar in fact consisted of three groups (1) the Madampis of "8 houses", who were essentially royal servants (Pandarakaryam Cheyvar), (2) Arukuttathil Pillaimar, who were the royal accountants from the 16th century onwards, and (3) two brahmana chiefs. The term Kanam, which implied overseeing or controlling right...