Tree cultivation. In the first millennium bce there was a remarkable expansion of fruit-tree cultivation in the Mediterranean from east to west. The productivity of Mediterranean *agriculture was significantly increased because trees were often intercropped with cereals and legumes, increasing total yields per unit area. These developments laid the economic foundations for the prosperity of Greek and Roman civilization and made diets more diverse and more nutritious. The most important of the trees in question were the *olive, vine (see wine), *fig, apple, pear, plum, pistachio, walnut, chestnut, carob, date-palm, peach, almond, pomegranate, sweet and sour cherry-trees. The cultivation of many of these species of trees depended on the spread of the technique of grafting. The date of the establishment of citrus trees in the Mediterranean is disputed. They were probably not important until after the end of the classical period. The Roman agronomists provide us with information about arboriculture. Trees were also very important in the ancient economy for *timber.