Factual error: In his flashback en route to Rome, young Lucius is shown playing football (soccer) as goalkeeper with his friends in Africa. There is no historic testimony of any ball game in the ancient world with such a close resemblance to modern soccer (exclusive use of feet, rectangular goal, etc.).
Suggested correction: There are a few seconds of kids kicking a ball (coconut) around and a kid guarding two poles. Nothing shows they are actually following the rules of modern soccer. They are not doing an official sport, just a ball game they came up with that happens to look like soccer. There is only one goal too.
It is not an official game, but it's not randomly kicking the ball. It's the way modern kids with a previous knowledge of football would organise. It seems trivial to us, even natural, but as you can see, for instance, on the FIFA website, it is anything but. Games with exclusive use of feet weren't a thing in the Greco-Roman world. What is shown in the movie is meant to resemble something that the modern audience is familiar with, but wasn't at all close to the culture of 2nd century kids in Egypt.
