By the late 19th-century, the caste system of Kerala had evolved to be the most complex to be found anywhere in India. There were over 500 groups represented in an elaborate structure of relationships and the concept of ritual pollution extended not merely to untouchability but even further, to unapproachability. The system was gradually reformed to some degree, with one of those reformers, Swami Vivekananda, having observed that it represented a "mad house" of castes. The usual four-tier Hindu caste system, involving the "varnas" of "Brahmin" (priest), "Kshatriya" (warrior), "Vaishya" (business person, involved in trading, entrepreneurship and finance) and "Shudra" (service person), did not exist. "Kshatriyas" were rare and the "Vaishyas" were not present at all. The roles left empty by the absence of these two ritual ranks were taken to some extent by a few Nairs and by non-Hindu immigrants, respectively.