Worldwide Flood 2: Heracleion Underwater City in Egypt

A whole city was in the river Nile delta close to Egypt. They found buildings, statues, potteries, ceramics and gold jewelry. They are telling us that the city has sunken... Really? Why would people in their right mind and with such an advanced culture and technology build on sand knowing it's not stable and going to sink? They were not insane like these historians! A clear proof for a worldwide flood creating the so-called mud flood (mud was most likely the residue of the flood).