There were no untouchables as documented by Greek Megasthenes (ca. 350 – 290 BCE). Caste according to him in India then.
The first is formed by the collective body of the Philosophers, which in point of number is inferior to the other classes, but in point of dignity preeminent over all. The philosopher who errs in his predictions incurs censure, and then observes silence for the rest of his life.
The second caste consists of the Husbandmen, who appear to be far more numerous than the others. They devote the whole of their time to tillage; nor would an enemy coming upon a husbandman at work on his land do him any harm, for men of this class, being regarded as public benefactors, are protected from all injury.
The third caste consists of the Shepherds and in general of all herdsmen who neither settle in towns nor in villages, but live in tents.
The fourth caste consists of the Artizans. Of these some are armourers, while others make the implements that husbandmen and others find useful in their different callings. This class is not only exempted from paying taxes, but even receives maintenance from the royal exchequer.
The fifth caste is the Military. It is well organized and equipped for war, holds the second place in point of numbers, and gives itself up to idleness and amusement in the times of peace. The entire force--men-at-arms, war-horses, war-elephants, and all--are maintained at the king's expense.
The sixth caste consists of the Overseers. It is their province to inquire into and superintend all that goes on in India, and make report to the king, or, where there is not a king, to the magistrates.
The seventh caste consists of the Councillors and Assessors,--of those who deliberate on public affairs. It is the smallest class, looking to number, but the most respected, on account of the high character and wisdom of its members; for from their ranks the advisers of the king are taken, and the treasurers, of the state, and the arbiters who settle disputes. The generals of the army also, and the chief magistrates, usually belong to this class.
This was also similar to the sayings of Xuanzang (c. 602–664) the Chinese scholar to traveled to India. There were no untouchables or poor.