Ennin's travel books are precious as historical sources, although they have some errors. His book was the first written document about China and its life by a foreigner. He did not write an evaluation of what he saw, but rather wrote about religious matters and Chinese life under the Tang Dynasty. His diary is a good source on the practice of popular Buddhism in China. He described ceremonies as well. He brought back many sutras and mandalas to Japan. He struggled in his travel during the Tang’s persecution of Buddhism (842-846).