No civilisation used the modern christian calendar so they never said themselves to be at a certain date like 300 bc. They had to be dated by historians in the 19th century. European historians believed the christian chronology that the flood event happened in 4004 bce and so it was used as an objective reference point to date civilisations. Ancient sumer is dated around 3000 bce and egypt a bit later when they were discovered in the 1700s. Greeks, alexander are dated from 1000-300 bce. Is it possible that since the biblical reference point they were using was based of a false premise, all of world history is dated incorrectly? Maybe ancient egypt was around in 5000 bce and greeks in 2000 bce.