Goofs

When Valiant spies on the Black Knight and the Viking chief on the beach, the Black Knight's visor is open when he's seen from behind, yet closed when cut to a shot of him seen from in front, then open again in the very next shot from behind.

As Prince Valiant leaves the Abbey and his parents to go to Camelot, he departs standing upright in a simple serving tray-shaped boat. As he shakily pushes off from the shore, one can clearly see a pontoon-like arrangement hidden under the craft, obviously designed to try to steady it. In later shots, pulled up on shore, it is flat-bottomed.

When Prince Valiant (Robert Wagner) is hiding underwater from the Black Knight, the reed through which he is breathing changes size between shots. When he first cuts it, it is so large in diameter it barely fits in his mouth, but in the next shot it is only half that size, easily discernible as a smaller reed than the original one.

The Black Knight has his shield on the right arm when first seen. In the next shot it is on his left, then in the next it's back on his right arm.

During the fight with Sligon, Prince Valiant managed to capture the Singing Sword and Sligon's body fell into the flames wearing the sheath. When Prince Valiant went to free his parents and other prisoners, he had both the sword and the un-burned sheath.

Vikings did not wear horned helmets.

The supposed era of King Arthur was the 5th century AD, perhaps even the 6th century AD. The Viking era stretched from the end of the 8th century AD to the 11th century AD. The difference between the two eras was at least two hundred years meaning that the movie's mixing of these two worlds never could have occurred.

Early in the movie, there is talk of bringing the Vikings back to Christianity. But if the setting is the 5th or 6th centuries AD, Vikings had yet to be Christianized. Therefore, if Vikings had yet to be converted, they could not have relapsed to pagans. And if they could not have relapsed to being pagans again, they could not be brought back to Christianity.

As Valiant leaves his castle to meet Boltar at the beginning of the movie, he jumps from several heights to the ground. As he jumps off a small hill next to the castle, one can clearly see mats falling down from the hill after he jumps.

During an elaborate fire stunt on a parapet, Prince Valiant turns to the camera for several seconds revealing that he is a stuntman and not Robert Wagner.

In the final sword fight between Prince Valiant and the Black Knight, Valiant swings and hits a wooden chair with his huge sword and doesn't even scratch it.

In this story set in the Middle Ages, Aleta and all the other women look as if they are wearing the notorious "torpedo bras'' of the 1950s.

The castle of Camelot is the type of castle that only came to be by the mid to later Middle Ages (12th to 15th centuries AD. In the 5th and 6th centuries AD, fortifications would have been wooden. Fortifications in England remained wooden through the early Norman Period (late 11th century). Norman fortifications in the early 12th century evolved to simple stone towers (as depicted in 1965's "The War Lord").

Though the setting is the 5th or 6th centuries AD, most of the knights wear helmets of the mid-Middle Ages (12th to 14th centuries AD).