Wikipedia
The Nagarathar (also known as Nattukkottai Chettiar) is a Tamil community that follows the belief system of Shaivism. The Brahmins consider them as a Vaishya (mercantile) caste and perform bramhin rites and rituals as well as the Ponool ceremony also known as Janeu and consider them as twice born Dwijas.
The Nagarathar or Nattukkottai Chettiar were historically an itinerant community of merchants but claim Chettinad as their traditional home. How they reached that place, which at the time comprised adjacent parts of the ancient states of Pudukkottai, Ramnad and Sivagangai, is uncertain, with various communal legends being recorded. Among those are a fairly recently recorded claim that they were driven there because of persecution by a Chola king and an older one, recounted to Edgar Thurston, that they were encouraged to go there by a Pandyan king who wanted to take advantage of their trading skills. The legends converge in saying that they obtained the use of nine temples, with each representing one exogamous part of the community.
They may have become maritime traders as far back as the 8th century CE, although this is not universally accepted. Certainly, they were trading in salt by the 17th century and European expansionism in South East Asia during the next century fostered conditions that enabled the community to expand its trading enterprises, including as moneylenders, thereafter.
In the 19th century, following the Permanent Settlement, some in the Nagarathar community wielded considerable influence in the affairs of the zamindar (landowners) elite. There had traditionally been a relationship between royalty and the community based on the premise that providing worthy service to royalty would result in the granting of high honours but this changed as the landowners increasingly needed to borrow money from the community in order to fight legal battles designed to retain their property and powers.