The period following the Greek colonial period, at least as far as Tokharestan is concerned - a country now encompassing Bactria and the south of ancient Sogdiana - is conventionally divided into several phases: the "invasion period" or "pre-Kushan" (from c. 145 BC to c. 50 AD); the period of the Great Kushans, named after the nomadic dynasty (Yuezhi) which reconstituted an empire that also extended to northern India (c. 50-230 AD); and the period of the Great Kushans, named after the nomadic dynasty (Yuezhi) that also extended to northern India (c. 50-230 AD).); the period of the Great Kushans, named after the dynasty of nomadic origin (Yuezhi) which reconstituted an empire that also extended to northern India (c. 50-230); a period of direct Sassanid domination (c. 230-280), followed by the period of the Kushano-Sassanid viceroyalty (c. 280-375); then came new invasions from the steppe, known as "Chionites", followed by an imperial reconstitution under the Kidarites and Hephtalites (c. 420-550). The chronology had long been the subject of great uncertainty, with, for the period of the Great Kushans, a wavering over two centuries in numismatic publications, which affected the conclusions of several Soviet excavators who dated the levels according to the coins, but it is now much more assured (a symposium was held in Berlin on December 5-7, 2013, which will lead to a book edited by Harry Falk).
The presentation temporarily abandons the big cities. They continue to exist (Bactria, Samarkand, Merv, Begram) or develop further (Termez), but the examples excavated do not offer as many possibilities as Nisa and Aï Khanoum for grasping the workings of urban organisms: these are all very long-lived sites, right up to the Islamic period, and for this reason the various periods, except for the last ones, are only partially known. Richer in cumulative information are the medium-sized cities, all of which developed from earlier sites (Achaemenid or Greek) and all of which suffered a major decline from the invasions of the 4thcentury onwards, or even earlier.
