Answer:
The Nile River
Step-by-step explanation:
Water during ancient civilizations was a MUST and looking at the most successful civilizations, you can see that they all are near a water source. The nice thing about water sources is that they provide silt, which is great for farming and makes the land fertile. They can also help with transportation because it was faster to go by boat than by horse and cart. This is the great thing about the Nile, it was the best of all of these things for the Egyptians. First, it provided them with water and food. This makes the basic needs for the civilization settled, so they can worry about advancement not surivival. Second, it provided silt for farmers making a surplus of food, which allowed for specialization (not everyone has to be a farmer). The silt was brought onto the farms though when the river flooded. The great thing though was that the river's flooding could be predicted because it happened at a certain time and would flood to a certain point on the river bank (unlike the Tigris and Euphrates Rivers for Mesopotamia). So, the Egyptians didn't have to worry about all of their stuff being destroyed. The final great thing about the Nile, was that sailing on the current of it, would lead you to the Mediterranean Sea, which was where all the trading went on, so the river really helped Egypt trade with other civilizations as well. This also allowed for cultural diffusion, so Egypt could impact others, but more importantly it could take ideas from other civilizations and implement them into it's own society (which it did quite often).