In short, art can express the essential qualities of a time and a place, and a study of it, clearly offers us a deeper understanding than can be found in most history books and enables us to learn more things about human society and civilization. The second point I'd like to make, is about the type of information. In history books, information is objective. That is facts about political，economical life of a country are given, but opinions are not expressed. Art on the other hand is subjective. It reflects personal emotions and opinions. For example, Francisco Goya was a great Spanish painter, and also perhaps the first truly political artist.