This is the irrigation system. It waters the crops and provides fresh water.
This is the arts. Metalworkers make cups, weapons, jewelry and mirrors
This is the social structure. The upper class / the top / consists of priests, land owners and government officials. In the middle / common class / consists of merchants, craftspeople, farmers and fisherman. Finally, at the very bottom were slaves.
This is the stable food supply. They used ox drawn plows to turn the soil to prepare it for planting. Before the plow was invented farmers used animal horns or pointed sticks to poke holes in the earth. They then would plant seeds in the whole. This method was a very slow way to farm. This is why they invented the plow.