Now men have different natures, and one man will do one thing better than many; and business waits for no man.

Hence there must be a division of labour into different employments; into wholesale and retail trade; into workers, and makers of workmen's tools; into shepherds and husbandmen.

A city which includes all this will have far exceeded the limit of four or five, and yet not be very large.

But then again imports will be required, and imports necessitate exports, and this implies variety of produce in order to attract the taste of purchasers; also merchants and ships.

In the city too we must have a market and money and retail trades; otherwise buyers and sellers will never meet, and the valuable time of the producers will be wasted in vain efforts at exchange.