Later, when the world was full of people who were evil, God chose to kill them and save only the animals and the most morally righteous person alive. He told a man, named Noah, to build a huge boat and gather two of every bird, mammal and lizard onto it. He was instructed to take 14, or a pair of 7, of clean animals. Only 2 of each could be unclean. Noah built and filled the boat as he was told, and a flood covered the whole world. After 40 days and nights, the rains stopped. Once the water had receded the boat landed on the mountain of Ararat. God promised never to send another such flood, and he used the rainbow as a sign of that promise.