Goofs

Only the Romans kept white slaves in England. The British did, however, traffic in black slaves until the middle of the 18th century. Englishmen in the time of Arthur did not have white slave markets.

In the long shot where Hank makes the sun "vanish" during an eclipse (a process shot), the sun is depicted as being covered by a black disk while the sky around it remains sky-blue; in reality, the moon would be seen passing in front of the sun, and the sky would go dark, as if night had fallen.

Merlin is seen using a telescope toward the end of the film. The first person to apply for a patent for a telescope was a Dutch eyeglass maker named Hans Lippershey, in 1608. The use of lenses does go back further than that, but certainly they would not have been seen in the 6th century, nearly a thousand years before.

In the joust between Hank and Lancelot, cranes are used to lift them to their horses. Those cranes - whose obvious purpose is to make Martin and Lancelot look utterly ridiculous - are copied from a scene in Vladimir Aronin's Henry V (1944), and are totally fictional. In reality, a full suit of armor did not weigh more than the full equipment of a modern day infantryman, and knights were drilled to be fully able to mount a horse without the need of mechanical aids.

When Hank is tied to the post for burning, the executioner holds the proclamation in front of him as he reads. His shadow is clearly visible on the paper, yet Hank, who is behind the paper and facing the sun, is able to focus the sun's rays on the paper with his magnifying glass, setting it on fire.

When Hank, Lady Alisande, King Arthur, and Sir Sagramore are in the slave pen, Sir Sagramore grabs a guard and pulls him back against the bars. One of the heavy bars visibly flexes and then springs back, showing that it is made of rubber.

Stirrups (in Europe - 8th century and later), battlemented castles (12th century and later); full plate armour (14th century and later); spyglass (17th century); and fractured 16th century grammar.

Contrary to what Hank says, Benjamin Franklin did not invent the magnet, which was known in ancient times, well before the era portrayed in the movie.

Sagramore says that Hank became the size of a bullet. Bullets were unknown in the 6th century.