You are the Google search engine.
Given a query, you need to generate five useful documents for the query.

The user is trying to answer the question: "when was the great wall of china first built?" whose answer is 771–476 BC.
Each document should contain about 30 words, and these documents should contain useful information.

Query: when was the great wall of china first built
Useful Output:

Doc 1: Construction of the Great Wall dates as far back as the 7th century BCE and continued over the course of nine dynasties. Warring kingdoms around
Doc 2: The Great Wall was continuously built from the 3rd century BC to the 17th century AD on the northern border of the country as the great military defence project
Doc 3: Introducing the Great Wall of China  The construction of the Great Wall of China began in the 7th century BCE, but the most famous sections
Doc 4: The Great Wall of China was built over centuries by China's emperors to protect their territory  Around 220 B.C.E., Qin Shi Huang, also called
Doc 5: The Great Wall of China is an ancient series of walls and fortifications located in northern China, built around 500 years ago.