Pyramids had a lot of value. Ancient people were superstitious to the highest degree, and knew that victory always goes to whoever is favoured by the Gods. So,

Pyramids had a lot of value. Ancient people were superstitious to the highest degree, and knew that victory always goes to whoever is favoured by the Gods. So, seeing these immense structures, Egypt's enemies knew that any raid on Egypt would be futile, as Egyptian gods would surely help their faithful followers who made them such magnificent gift.