 Complete the following phrase:  Players can also build Wonders of the World in each of the epochs of the game, subject only to obtaining the prerequisite knowledge. These wonders are important achievements of society, science, culture and defense, ranging from the Pyramids and the Great Wall in the Ancient age, to Copernicus Observatory and Magellans Expedition in the middle period, up to the Apollo program, the United Nations, and the Manhattan Project in the modern era. Each wonder can only be built once in the world, and requires a lot of resources to build, far more than most other city buildings or units. Wonders provide unique benefits to the controlling civilization. For example, Magellans Expedition increases the movement rate of naval units. Wonders typically affect either the city in which they are built for example, the Colossus, every city on the continent for example, J.S. Bachs Cathedral, or the civilization as a whole for example, 