The Greeks set a trap for the Persian fleet, spiked poles under the water. As the Persian fleet approaches and hits the first spiked pole, it comes THROUGH THE SIDE, rather than through the bottom where it's placed.
When Philippides and the Imperial Guards are setting up the spikes on the beach, a tanker ship can be seen in the far distance, the left of the screen.
At 44:17, the stunt rider meant to represent an enemy attacker is much darker than the actor he's doubling.