Why were walnuts not allowed to be eaten by commoners in Babylon?

The history of walnuts (in this case the English walnut) is as old as the stories of almonds and pistachios. In fact, ancient inscriptions suggest walnut trees were grown in the Hanging Gardens of Babylon. Walnuts were also a valued staple in the diet of ancient Greeks and Romans.

The walnut even has a place in Greek mythology, as the god Dionysus turned his love, Carya, into a walnut tree after she died. Romans also considered walnuts food for the gods, while mere mortal citizens of Rome used walnut oil and walnut flour. Walnut oil was used extensively in the Middle Ages, and peasants ground up walnut shells to make bread. Walnuts made their way to the New World sooner than pistachios, arriving with Spanish priests in California during the 18th century.

The tough-shelled black walnut hit the world stage much later than its thin-shelled relative. This variety is also known as the American walnut and is believed to be native to North America. Historical records indicate black walnut wood was shipped to England from Virginia in about 1610.