From time immemorial all castes have not been treated equal in rank and status. In the hierarchical ladder the Brahmins have always been considered and placed at the top. All other sections and castes in the society have been asked to respect Brahmins.
Even in the olden days when Kshatriyas ruled the country, in Royal Courts Brahmins enjoyed a very high and unique position. Similarly one finds that a woman was required to attend to Brahmin asking for alms first than to her hungry and thirsty husband.
Next in rank then came the Kshatriyas whose main duty and responsibility was to defend the nation from outside aggression. They ruled no doubt but it was always provided that they should rule according to Dharma. Whether domain was being ruled according to Dharma or not was the prerogative of Brahmins to decide. Next in the rank then came the Vaishyas, who were cultivators engaged in business, trade, commerce and so on. It was their foremost duty to serve to the needs and requirements of first two high ranking castes.
And at end of the ladder were, of course, the poor and the cursed Shudras. They had no social status. They were supposed privilege. Their coming to the town without prior intimation was banned. Not only that they lived outside the town but their shadow on the high caste polluted them.