The main reason for the wall's construction had always been defense. Since China's first dynasty, the empire faced a near-constant threat of attack from the nomadic tribes to the north. This included those famed Mongols as well as lesser-known groups like the Xiongnu and the Göktürks.
The earths most important energy sources the sun
The hubble telescope thing
If you are referring to the countries surrounding the Mediterranean sea, the answer would be Egypt with a population of about 82,079,636, give or take a few. The second most populated country on the Mediterranean would be Turkey, with a population of 78,785,548.
