Until recently, Achaemenid historiography did not show much interest in the reign of Darius III, or in the state of the empire at the time Alexander set foot in Asia Minor. It sufficed to explain everything by the convenient thesis of the "colossus with feet of clay" that had become irreversibly undermined by disorganization, overtaxation, and rebellious subjects. This thesis was, in itself, deemed sufficient to explain the Persian defeat in confrontations with the Macedonian armies. From its origins, Alexander historiography has developed two visions of the Persian adversary. One is found in handbooks and the most recent conference proceedings: that the Achaemenid empire is evanescent to such a degree that it does not even represent one of two players in the game about to be played on the Near Eastern chessboard: time passes "as if Alexander were alone...when he faced his personal quest." In contrast, other historians have attempted to reevaluate the military strategic capacities of the last Great King.
This double orientation in modern historiography is, to some extent, the latest avatar of a double-sided image of Darius handed down by the Greco-Roman tradition and continuously running through modern European historiography: Darius is either portrayed as a despot characterized by weakness and lack of drive, a man incapable of facing the danger that the Macedonian invasion presented to his throne and his empire; or he is glorified as a king possessing virtues and all kinds of admirable qualities, yet confronted by an enemy of such overwhelming strength that he stood no chance of gaining victory over him. This second image, of a man both capable and courageous but overcome by a peerless adversary (presented by Bossuetas early as 1681), was adopted by Droysen from 1833 on, and the same conclusion is reached by a recent study by Badian (2000b: 265)
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(c) Pierre Briant: Collège de France, Chaire d'histoire et civilisation du monde achéménide et de l'empire d'Alexandre and Emeritus