When Antillia steals the boat, the background shows the sea with normal waves. When Demetrios swims out to the boat the water is extremely calm. This also gives away the fact that the shot of Hall swimming was done in a studio tank.
The triangular pit of fire and water loses an acute angle during close ups of the fight. A flat wall replaces the 60 degree corner.
Demetrios tells Antillia that the Greeks have no slaves. This was not true.
Demetrius states that he had a dream about Neptune. He is Greek, and he would not have known about Neptune. The Greek god of the sea was Poseidon, not Neptune who was the Roman counterpart of the Greek sea god.
Obvious stunt double for Demetrios during the Ordeal of Fire and Water and the rope-hanging scene.
When the priest demonstrates the model crystal and uses it to destroy a vase, the vase melts. As the last part melts a round hole used to pump hot air up into the wax vase can be seen beneath it.
When Demetrios is visited by Antilla in his tent a round smallpox vaccination scar is clearly visible on his left arm.
In the House of Fear, a domestic hog appears. Breeders did not start to develop what we know today as the domestic pig until the 18th century of the Common Era (CE). Before that, domestic swine were almost identical to wild hogs: sharply defined backs, lots of bristly body hair, and very big tusks in their mouths.
Demetrios's fishing boat with the triangular sail and stern rudder was a type of craft that didn't appear until the Byzantine era, ca 1100 AD.
At the time line of Atlantis-ca. 10,000 BC , there was no Greek civilization as we know it. Since so many set pieces from "Quo Vadis" were used, this pushes the time line to the 1st. century AD.
After the rescue of Antilla, Demetrios asks her from where she came. She answers that her land is "beyond the Columns of Hercules". But in time of Atlantis (9000b.C) Hercules hasn't done this job or even has been born (1500 to 1200 BCE).