eventually disintegrated by the usual action of specialist 
trading and the separation of functions that Mumford portrays 
in The City in History . The Roman cities began that way—as 
specialist operations of the central power. The Greek cities 
ended that way.

     If a city undertakes rural trade, it sets up at once a 
centre- margin relation with the rural area in question. That 
relation involves taking staples and raw produce from the 
country in exchange for specialist products of the craftsman. 
If, on the other hand, the same city attempts to engage in 
overseas trade, it is more natural to “seed” another city centre, 
as the Greeks did, rather than to deal with the overseas area as 
a specialized margin or raw material supply.

     A brief review of the structural changes in the