The written sources are the main historical source that historian use in their research. However the answers they provide will very much depend on the sorts of questions historians are asking. Before we start reading the text, we should ask Who is the writer? The writer's background will define our attitude towards the text. For example, Procopius of Caesarea, the writer of the Wars of Justinian, was the legal adviser of Justinian's chief military commander and followed him in the battlefield. Therefore, we can gain from his book valuable information about the structure and the war technique of the Easter Medieval army. On the other hand, we know that he was devotee to the Byzantine royal family, so he try to compliment the Emperor with his books. Another question is When was the text written? And finally, Where was the text written?.By using these three questions we are able to create a "safety net" while we are making our conclusions .