"The technologies which have had the most profound effects on human life are usually simple. A good example of a simple technology with profound historical consequences is hay. ... It was hay that allowed populations to grow and civilizations to flourish among the forests of Northern Europe. Hay moved the greatness of Rome to Paris and London, and later to Berlin and Moscow and New York. [The year-round growth of green grass in the Mediterranean climate meant that hay was not needed by the Romans. North of the Alps, hay maintained horses and oxen and thus their motive power, and productivity.]"