Brahmins did not invent castes. It was brought in by incoming people belonging to different cultures and nations into India . In India they were not forced or encouraged forcefully to lose their identity and culture unlike in the present day US or UK. Hence they continued with their culture i.e castes.
For example if you take TN alone and look jus the number of backward castes ( not sc , st or mbc ), we have 140 odd castes
http://www.tn.gov.in/department/bclist.htm
There are castes called as karpura chettiar , kasukkara chettiar etc . They mean camphor chettiar and cash chettiar-- chettiar is equivalent to seth in the north .
Now where in the hindu scriptures are such castes mentioned?
Nowhere. Clearly caste is not an invention of the Brahmins. The Brahmins only tired to integrate such people belonging to different culture groups called caste . They integrated them into Indian society.
