Ancient history is, first of all, a written history based on the following sources: documents, manuscripts, printed books, paintings, monuments, and artifacts. When a school textbook tells us that Genghis Khan in year XXX A.D or Alexander the Great in the year YYY B.C. have each conquered half of the world, it means only that it is so said in some of the written sources. Seemingly simple questions practically never have clear, unambiguous answers. When were these sources written? Where and by whom were they found? For each of these questions, the answers are very complex and require in-depth research.It is further WRONGLY presumed that there are numerous carefully preserved ancient and medieval chronicles readily available, written by Genghis Khan's or Alexander the Great contemporaries and eyewitnesses to their fantastic conquests, which are kept today in the National Library of Republic of Mongolia or Greece; or in the Library of Congress, or in the private collection of Microsoft. Zilch comma zilch sources come from contemporaries and eyewitnesses: Mongols were a nomad and illiterate bunch, sweet Alexander lived so long ago that most 100% reliable sources know for sure he was the son of Zeus, right? Wrong, we have not seen Alexander