Factual error: In chapter IX "Friend of the Gracchi", Tiberius Gracchus writes a letter home just after the destruction of Carthage, saying the farmland was plowed under with salt, to prevent anything from growing there. But recent (21st century) studies have shown that no record of such an event exists, and that the story of the salting of Carthage is a 20th century fabrication, made more than 2000 years after Tiberius Gracchus lived.
Factual error: In chapter XI, "Caesar's Heir", the murder of Julius Caesar is depicted taking place in the Senate Hall. But in reality, the assassins abandoned this plan, and instead lured Caesar into the portico of a nearby theatre and killed him there.