When the crew is climbing up to the bell, the ship is shown anchored in a different place to their landing site, i.e. they landed on a beach yet there is no beach visible below them, just a rocky shore.
When the Vikings fight the Moors on the beach, they throw spears and shoot arrows killing many Moors. However, none of the arrows or spears can be seen in flight nor can any be seen hitting the Moorish cavalry (who fall and die).
When Aly Mansuh is crushed by the golden bell, it rolls onto his body at waist level. In succeeding shots, it is shown laying across his chest.
As the ship approaches, the bell dome is shown at the top of a sheer cliff. Yet everyone climbs a gentler slope than the vertical cliff initially shown.
After the Vikings and Moors get through the maelstrom, despite nearly tipping over and lots of water flowing over the ship, when Poitier looks up at Widmark, the deck is clearly dry.
Gold, like lead, is a soft and non-resonating material. A bell made of solid gold would "clunk" rather than ring.
The "golden" bell floats far too high in the water after it falls down the cliff and several of the "bodies" it pulls off the cliff are ahead of it in at least one shot.
Even though gold is a very soft metal, at no time after it rolls down the cliff is there a dent, or even a scratch, appearing anywhere on the surface. When it is brought into the city, it is in mint condition.
Ten times the number of men shown could not lift the bell of gold; nor could the small raft shown float it.
Leaving aside the issue of the sound of a bell made of gold, the bell could not the sound it does. It forms the dome of the building and is covered with concrete and stone which would stop the metal vibrating, absorbing the energy of the sound.
King Harald's "fleet" is embarrassingly small, more befitting a thane than the King of Denmark. However, this is no doubt a budgetary issue.
When the bell falls from its supports the small chains holding it snap. It is no longer attached to the men who are, regardless, pulled down after it.
When the golden 'prop' bell breaks loose and rolls down the cliff, the entire top mount gets smashed and the top of the bell peels open. Yet after that during the free-fall to the water and beyond, it is back to mint condition.
Several times during the story the bell is described as being "the height of three tall men". Once it shows up on the screen it's actually only the height of two tall men.
A gag is placed in Gerda's mouth and all she does is thrash her head from side to side. The normal reaction would be to rip the cloth off with her free hands and turn around to see her attacker. Stupid.
The model ship Mansuh is holding early in the film is of a type of galley that wasn't built until the late 17th century in France, some 700 years after the story takes place.
One of the Vikings fighting the Moors on the beach is wearing bright white underpants.
When Princess Gerda is summoned by King Aly Mansuh in his chambers, a clear inoculation scar is visible in her right arm.
Rolfe apparently swims back to Denmark from North Africa, a distance of over two thousand nautical miles.
All the Vikings and all the Moors (including the harem) seem to either be speaking the same language, or all be fluently bilingual.