Guoqing Yang is deputy research director at the Center for the Protection of the City Wall of Nanjing. For 15 years he has been engaged in the research of the city wall. His results have been pub-lished in the form of articles, essays and monographs. In 2011, at the invitation of the Institute for the History of Science of the Max Planck Institute, Yang conduct-ed a comparative study in Germany on the history and current situation of the city walls in China and Germany.