Birth of Cities From 4000 to 1000 B.C., agricultural communities flourished throughout Eurasia with systematic irrigation supporting ever-larger populations in the fertile valleys of the Nile, Tigris, Indus, Euphrates and Yellow Rivers. Here, the first cities were born to house the diverse trades coming into being – farmers, builders, those who stored, accounted for and sold surpluses. The administrative and commercial needs led to the rise of class differentiation and bureaucracies, then merchants, traders, priests, princes and kings. Ever larger storehouses and public buildings, then palaces, were constructed as well as a variety of dwellings according to the requirements of the variety of emerging classes. The lifting of earth and stone to create cities and their contents became as important as the elevating of water for the fields. The accumulation of wealth drew the attention of less affluent neighbors who developed means of storming cities for booty and for slaves to provide their manpower. The cities responded with the building of ever thicker and higher defense walls and the creation of increasingly efficient construction tools and mechanisms. Better defenses led to improved offenses and a race began that had no end throughout history. Successes in conflict led to consolidations – small kingdoms, then powerful states and nations with rulers who required ever-higher monuments. Most structural memorials were to personalities; others to gods, then to God.