The three-field system first appeared in the eighth century and was adopted so widely and rapidly that during the nineteenth century many historians erroneously assumed it dated from Roman times. But the Romans knew only a two-field system of agriculture, because they did not know that legumes helped to restore the land, and thus land needed to lie fallow less often. Thus, half of their land lay fallow each year, compared with one-third under the medieval three-field system.27 Not only did most Europeans eat far better during the Dark Ages than in Roman times but they were healthier, more
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