<Dd> The Persian Empire is an empire in the modern sense--like that which existed in Germany, and the great imperial realm under the sway of Napoleon; for we find it consisting of a number of states, which are indeed dependent, but which have retained their own individuality, their manners, and laws . The general enactments, binding upon all, did not infringe upon their political and social idiosyncrasies, but even protected and maintained them; so that each of the nations that constitute the whole, had its own form of constitution . As light illuminates everything--imparting to each object a peculiar vitality--so the Persian Empire extends over a multitude of nations, and leaves to each one its particular character . Some have even kings of their own; each one its distinct language, arms, way of life and customs . All this diversity coexists harmoniously under the impartial dominion of Light...a combination of peoples--leaving each of them free . Thereby, a stop is put to that barbarism and ferocity with which the nations had been wont to carry on their destructive feuds . </Dd> <P> American Orientalist Arthur Upham Pope (1881--1969) said: "The western world has a vast unpaid debt to the Persian Civilization!" </P> <P> Will Durant, the American historian and philosopher, during one of his speeches, "Persia in the History of Civilization", as an address before the Iran--America Society in Tehran on 21 April 1948, stated: </P> <Dl> <Dd> For thousands of years Persians have been creating beauty . Sixteen centuries before Christ there went from these regions or near it...You have been here a kind of watershed of civilization, pouring your blood and thought and art and religion eastward and westward into the world...I need not rehearse for you again the achievements of your Achaemenid period . Then for the first time in known history an empire almost as extensive as the United States received an orderly government, a competence of administration, a web of swift communications, a security of movement by men and goods on majestic roads, equaled before our time only by the zenith of Imperial Rome . </Dd> </Dl>

When was the persian empire at its height in power