Factual error: The backdrop to the party scene in India shows a large building with glass windows. The Romans were the first to use glass windows some 300 years later.
Factual error: Just before old Ptolemy starts telling his story of Alexander, at the very beginning of the movie, we see a shot of the famous Lighthouse of Alexandria. It's fully operational, which is a mistake because the building was finished during the reign of Ptolemy's son, Ptolemy II Philadelphos, some years after the first Ptolemy's death.
Factual error: Contrary to what's depicted in the movie, Cleitus was never involved in the murder of Parmenion. He was in fact on his way to Alexander when Parmenion was killed.
Factual error: The event of wounding Alexander by an arrow that punctured his lung is depicted with great attention to detail and shown exactly as described by historians. However, in reality, it happened during the storming of the Mallian Stronghold, not during the battle of Hydaspes.