Choir stalls or fixed seating
The general thinking is that a law is unjust if it doesn't square with natural law. This is certainly the view that was put forth in Martin Luther King's Letter from Birmingham Jail.
So, a law that was passed that treated people differently wouldn't square with the natural law that all humans are equal. And thus, one would have the obligation to disobey that law.
The Indus River valley civilization was a theocracy run by a priest and karma played a very big role in their laws
The civilization was plolythiestic and was made up of Hinduism bhudism and Jainism
The economy was based on agriculture and trade with the people there making items like cloth and pottery
The social hierarchy went like this
Gods
Kshatryia
Vaishya
Sudra
And then the untouchables