People first began to settle and farm the flat, swampy lands in southern Mesopotamia before 4500 b.c. Around 3300 b.c, people that were called Sumerians settled in Mesopotamia. Good soil was the advantage that attracted these settlers. Fertile soil is ideal for farming and growing crops. Another advantage was the Tigris and Euphrates rivers that provided water for irrigation and trade. The disadvantage of the geography of Mesopotamia is that there was unpredictable flooding combined with a period of little or no rain. The land sometimes became almost a desert which affected the production of crops. Another disadvantage was that there were no natural barriers for protection which left the Sumerians nearly defenseless. Over a long period of time, the people of Sumer created solutions to deal with these disadvantages. To provide water when there was little or no rain, they dug irrigation ditches that carried river water to their fields and allowed them to produce a surplus of crops. For defense, they built city walls with mud bricks.