At its height the Persian empire covered over three million square miles and spanned across three continents (Asia, Africa and Europe). It has been estimated that in the year 480 BC about fifty million people or %44 of the world's population lived under the rule of the Persians. The empire extended from India on the east all the way to Africa on the west and was the largest empire the world had ever seen until that time.
The Talmud records a dispute if Hodu and Cush were on opposite ends of the world or right next to each other. The word Hodu is commonly translated as India and Cush is thought to be Ethiopia which is in Africa. The Persian empire certainly extended that far.