Great Wall of China:a large strong wall that is over 2000 kilometres long and which was built across northern China to protect the country against enemy armies. It was originally built in the 3rd century BC, but only a few parts of that original wall remain, and most of the wall we see today was built in the 15th and 16th centuries. Many people think that it is the only structure built by humans that can be seen from space, but this is not true.——Longman Dictionary of Contemporary English  @en