The shape that could be used to describe the structure of social classes in early civilizations is the pyramid. In the absence of social classes the whole system will break down, and the social classes provide basis for a successful civilization.
The uppermost class was of the Brahmins, followed by Kshatriyas, Vaishyas, Shudras, Untouchables and last came the Adivasis.
The shape you could use would be a triangle and/or pyramid. the higher classes (such as monarchs and priests) would be at the top of the triangle / pyramid and the lower classes (such as farmers and pheasants) would be at the bottom of the triangle / pyramid.
