China is a vast country with a huge range of terrains and climates within it: mountains, deserts and coastlands and above all, the great river systems of China, the Yellow River to the north and the Yangtze to the south. All these have helped shape Chinese civilization. The civilization of ancient China first developed in the Yellow River region of northern China, in the 3rd and 2nd millennia BCE. This is a very fertile region; however the land needs irrigation to make the crops grow, and well-built river embankments to prevent catastrophic flooding. In ancient times, the main crop in northern China was millet, a food still grown in many parts of the world as a major crop. This region is regarded as the Cradle of China’s Civilization. It was here that the earliest Chinese dynasties were based. Throughout the ancient period of China’s history it formed the heart of the Chinese world, and it was from here that Chinese civilization spread out across the rest of China.