Factual error: In this episode we see Blithe get shot in the neck and are told that he died in 1948. In reality he was shot in the shoulder and survived. He later served in Korea and was promoted to master sergeant as well as receiving the paratrooper of the year award. Blithe died in 1967 while on active duty in Germany.
Factual error: Aetius' troops don't look anything like 5th century Roman soldiers. They are carrying a large rectangular shield, a pilum (a spear which was used for throwing) and a sword (gladius) on their right. This was typical for the Roman army until about the 3rd century A.D. In Aetius' time, the soldiers would have had smaller oval shields, a hasta (a lance used for stabbing and for fending off cavalry attacks) and a sword (spatha) on their left. Also, there would be an enormous amount of "barbarian" mercenaries in the Roman army (Goths, Vandals, even Huns.), so it was hardly a Roman army anymore. And where's Aetius' cavalry?
Factual error: The American flag shown waving outside the White House is the current present-day flag with 50 stars. From 1896 to 1908, (the time period that this show is set in) the US flag only had 45 stars as Oklahoma, New Mexico, Nebraska, Alaska and Hawaii were not recognised as states in that time period. The flag did not have 50 stars until 1960. (00:04:30)
Factual error: Disc 2: There is a scene where a cannon shell explodes inside a hospital ward. Everyone in the ward is killed, but there are no signs of limbs torn off or even shrapnel wounds, only some blood here and there. The same thing happens at the Battle of Bull Run when the old woman gets blown out of her bedroom by cannon fire. (01:32:00)
Factual error: "Underground" is set in 1857 Georgia, yet the padded baseball glove August Pullman gives to his son is of a type used during the early 20th century. Before 1883 when padded gloves were first manufactured, gloves were either not used by baseball players or railroad brakeman's gloves were used.
Factual error: Once the Queen has given Mr. Churchill his "dressing down", he simply turns to leave the room. However, he had not been dismissed. The Queen always pushes a button positioned on a side table to call her equerry who enters the room to escort guests out. With Mr. Churchill, she did not request her equerry. (00:54:00)
Factual error: When they first meet, Rodrigues tells Blackthorne that aboard his ship there is plenty of food and grog. The problem is that grog was not "invented" until 1740, when it was introduced into the British Navy by Admiral Edward Vernon, who was nicknamed "Old Grog" because of his habit of wearing a grogram coat.