Director Doug Lefler managed to get all of the family of Thomas Brodie-Sangster in the film (uncredited). At 01:01:10 Thomas' mother Anastasia is shown hugging Kustennin, commander of the Ninth Legion, and again at 01:09:40 as Ygraine's mother. At 01:03:25 Thomas' younger sister Ava is shown as the first Celtic girl in the scene where Ambrosinus explains the heritage of Caesar's sword. At 01:10:48 in the background by Kunstennin, as the blacksmith begins stating his view of Romulus living among them, is Thomas' father Mark.
The invention of stirrups did not reach the Roman Empire. This invention arrived only after the fall of their reign, around the 7th century. As such the horsemen could not have used stirrups as seen in this film.
In the fight at the island fortress where Romulus is being held prisoner, Mira fights a horde of Goth guards, killing them all. However, as she stands amid the bodies of the Goths she has just hacked, slashed and stabbed to death, there isn't a drop of blood on the sword or the large dagger she used to kill them.