In the eighteenth-century dispute about the populousness of ancient nations (one particular skirmish in the general battle of the books) we have seen that Malthus declares for the moderns. He gives his opinion in detached passages; but, putting together the different parts wherever we can find them, we discover his proof to depend on two principles, which are corollaries of the primary doctrine of the essay. The first is, that without the extension of agriculture or the better distribution of its fruits there can be no increase of population;[212] the second is, that whatever is unfavourable to industry is to that extent unfavourable to population.[213] Now in the early days of Greece and Rome[214] the population ought on these principles to have been a large one, for not only was agriculture actively prosecuted, but property and wealth were more equally divided among the people than in later times. On the other hand, the numbers were always up to the level of the resources; and the smallness of the political divisions made law-givers like Solon, and theorists like Plato and Aristotle, conscious of the risk of over-population and full of plans to provide against it. It is one of Aristotle’s criticisms of Plato’s Republic that Plato has not sufficiently met this difficulty, or realized that a community of goods or an equal distribution of property is impossible without a limitation of families. If every one may have as many children as he pleases, the result will soon be poverty and sedition. Of the preventive checks actually recommended by the highest wisdom of the Greek world, the mildest is late marriages; the rest include exposure and abortion. Colonization was rather adopted in practice than recommended in theory. Frequent wars and occasional plagues were the chief positive checks. In Rome even more evidently than in Greece[215] the causes that produced inequality of property led also to thinness of population. In our own days the absorption of small proprietors by large would have this effect in a less degree, because the large would need to employ the labour of the small. In Rome the labour was done by slaves; and the wonder was not that the number of free citizens should decrease, but that any should exist at all, except the proprietors.[216]