After the attack on the Trojans' camp, the Trojans carry the dead from the field. One of the dead bodies lying on the ground with a spear in his back all of a sudden crosses his feet.
Early in the movie, an army is seen passing by a maize field; this plant, however, was cultivated in Europe only since 1525, having been brought to the continent by Christopher Columbus.
During the riding and shooting contest, the characters' horses are equipped with stirrups. Stirrups were unknown in Europe during the B.C. era.
During the revolt at King Latino's palace, Steve Reeves's stand-in (who by the way is clearly a different man with curly, ruffled hair) lifts two opponents and throws them back. During the whole scene, the wires they are hanging from are blatantly obvious.