 The former region of Gandhara and Kamboja (upper Indus) had constituted seventh satrapy of the Achaemenid Empire and annually contributed 170 talents of gold dust as a tribute to the Achaemenids.Bactria had a special position in old Afghanistan, being the capital of a vice-kingdom.By the 4th century BC, Persian control of outlying areas and the internal cohesion of the empire had become somewhat tenuous.