William Lindesay is collecting garbage at the Jiankou section of the Great Wall during a cleanup event held on April 22. [Photo/China.org.cn]

"It's a good thing that people are going out to enjoy themselves and to discover the great heritage and history, but it's also quite dangerous if they don't understand how fragile the environment is and how fragile the antiquities are," William said.

"Every person can make a difference. If we can get a billion Chinese people to be environmentalists, China will be a green, beautiful and healthy country to live in," he said.

William believes that in order to get people passionate about the Great Wall, they need to know more about it and its history.

In 1989, his first book Alone on the Great Wall was published, and he has published another five books about the Great Wall since then. In 2001, he founded International Friends of the Great Wall, an association whose efforts are aimed at protecting this link to the past.

His next step is to organize exhibitions about the Great Wall as a monument over the last 400 years. The exhibitions are expected to be held in Beijing, London, Paris and Washington DC.

The cleanup event, started in 2002, is sponsored by BLACK YAK, a Korean outdoor clothing and equipment company also actively striving to protect the environment.