From the Indus to the Mediterranean Sea: the Administrative Organization and Logistics of the Great Roads of the Achaemenid Empire

From the Indus Valley in the east and the Aegean coast in the west, from the Iaxartes/Syr Darya river in the north to the Aswan in the south, the Persian Achaemenid empire, for more than two centuries, was the largest empire ever put together in antiquity. During a decade of conquest, Alexander had constituted it precisely to his advantage by appropriating the same boundaries (Elephantine, Syr Darya, and Indus). Already in antiquity, Greek observers highlighted what they regarded as one of the major problems of imperial government: the contrast between the immensity of imperial territories and the will of the Great Kings to establish and maintain their hold. 

(c) Pierre Briant: Collège de France, Chaire d'histoire et civilisation du monde achéménide et de l'empire d'Alexandre and Emeritus
Source: Academia.edu