Xenonophon, precursor of Adam Smith

Via a passing reference in Marginal Revolution I get to a Wikipedia article on who first described the principle of the division of labor leading to improved efficiency and effectiveness. It is close run between Plato and Xenophon though my money is on Xenophon as being the more explicit. From Wikipedia.

Plato

In Plato's Republic, the origin of the state lies in the natural inequality of humanity, which is embodied in the division of labour.

Well then, how will our state supply these needs? It will need a farmer, a builder, and a weaver, and also, I think, a shoemaker and one or two others to provide for our bodily needs. So that the minimum state would consist of four or five men.... (The Republic, p. 103, Penguin Classics edition.)

Silvermintz notes that, "Historians of economic thought credit Plato, primarily on account of arguments advanced in his Republic, as an early proponent of the division of labour." Notwithstanding this, Silvermintz argues that, "While Plato recognizes both the economic and political benefits of the division of labour, he ultimately critiques this form of economic arrangement insofar as it hinders the individual from ordering his own soul by cultivating acquisitive motives over prudence and reason."

Xenophon

Xenophon, in the fourth century BC, makes a passing reference to division of labour in his 'Cyropaedia' (a.k.a. Education of Cyrus).

Just as the various trades are most highly developed in large cities, in the same way food at the palace is prepared in a far superior manner. In small towns the same man makes couches, doors, ploughs and tables, and often he even builds houses, and still he is thankful if only he can find enough work to support himself. And it is impossible for a man of many trades to do all of them well. In large cities, however, because many make demands on each trade, one alone is enough to support a man, and often less than one: for instance one man makes shoes for men, another for women, there are places even where one man earns a living just by mending shoes, another by cutting them out, another just by sewing the uppers together, while there is another who performs none of these operations but assembles the parts, Of necessity, he who pursues a very specialised task will do it best.

Xenonophon, precursor of Adam Smith.