Alexander the Great’s empire, which stretched from the Danube and the western shore of the Black Sea in the north to the Indus valley and Indian Ocean in the east, did not survive his death. Competition among his successors involved almost constant warfare, strategies to secure desirable commodities, and a nearly insatiable need for cash reserves. Whereas the founders of the new kingdoms were predominantly cavalrymen, the soldiers of succeeding generations were armed settlers and frontiersmen. The technology of warfare also underwent rapid changes at the start of the Hellenistic era, when siege machinery and artillery were introduced. Maintaining empires required different armies and resources, bringing wealth to countryside as well as city.The organizational template created by cities in the 4th century bce provided an efficient and flexible model of economic as well as social organization that enabled cities of all cultural and linguistic origins to become focal points of economic expansion under the kingdoms of .