History of the Universe eBook. 398 pages, 300 illustrations only $2.99
7000 to 5000 years ago was the warmest time of the , much warmer than now. Plants and villages grew quickly. In Iraq and Egypt, in and , there were river valleys which flooded every spring and replaced the minerals of the soil. These valleys stayed fertile for many years. Villages here grew into cities.
The settled way of life led to an increase in food production and population. It also let people specialize in one job, and this led to many inventions: tools; clay pottery and bricks; wheels; cast bronze tools and weapons; reading and writing. From the earliest writing we know a little about how these cities worked.
At first, cities were led by priest-kings. Later, when fighting with nomads and other cities became more important, the jobs of king and priest became separated. These leaders learnt how to organize people to build canals, city walls, temples and grain stores to carry the city through crop failures. The made laws which were written down. Astronomer-priests learnt how to use the stars to work out when the floods would come and when to plant seeds. Others discovered mathematics and used it to plan new buildings.
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