Continuity mistake: One of the first shots in the picture is a wide angle establishing shot showing a street scene in Jerusalem, with milling people, animals, etc. A tall figure in the background is slowly walking toward the camera. The figure is Charlton Heston, and the shot is an earlier segment of a shot used later in the movie when Ben-Hur is returning home from a trade expedition. Heston's costume is the same, but he's only clearly recognizable in the second sequence. Since the two scenes are set 33 years apart, perhaps the earlier figure is Ben-Hur's father.
Continuity mistake: When Judah takes rest on his way to Jerusalem funny things happen with his headgear. First, when he lies down it suddenly disappears under his head. Then he falls asleep, and when Balthasar from Alexandria approaches him a little later and he quickly gets up there is nothing under his head and back.
Deliberate mistake: During the chariot race, the chariots crash together but the arrangement of the horses make it impossible for them to actually collide. In some instances (particularly in an aerial shot as Ben Hur and Messala round the turn) it is obvious that they repositioned the shaft of the chariot to between the first and third horses instead of being in the centre between the second and third.
Continuity mistake: During Ben Hur and Messala's duel on the chariots, Messala's wheel-scythes tear away most of the right hand side of Ben Hur's chariot. When Messala has been thrown and Ben Hur crosses the finish line a few moments later, however, the camera has zoomed out far enough to reveal that his chariot is perfectly intact.
Factual error: The galley during the battle scene is rowed by slaves. Romans during this time period didn't use slaves to row their galleys. Rowers had to be able fight. If not, the Romans would be outnumbered 200 to 30 when they boarded the pirate ship as the pirates rowers would be able to fight.
Factual error: The actors and stunt drivers use only two reins to control the four horses that pull each chariot in the race. However, charioteers in ancient Rome used separate harnesses with two reins controlling each horse. In a race such as the one depicted in the movie, where four horses draw the chariot (two-horse races were common, as well), a real charioteer from the era would be holding eight reins.
Factual error: Al-Tair and al-Deberan are the names of the Arab Sheikh's horses, and he states they're named after the stars. Those stars were given their names by Arabian astronomers, and calculated astronomy by the Arabs emerged during medieval Islam in the 7th and 8th century CE, 674 years after the plot of the movie takes place.
Continuity mistake: At the end of the chariot race, a heavily bloodsoaked Messala is taken to receive medical treatment. While something is done to his legs out of shot (amputation, presumably) an orderly in a clean white tunic leans his whole body weight on Messala to hold him down on the bed as he writhes in agony. When the orderly stands up, we see that his tunic is still spotlessly white.
Continuity mistake: Right before the chariot race, Sheik Ilderim is on Judah's left side, pointing out the spikes on Messala's wheels. There's a shot of the wheels and then back to Judah, where the Sheik is now on Judah's right side. Judah holds the Sheik's forearm as the fanfare starts. Then a long shot, showing the Sheik, now on Judah's left side again, and Judah removing his hand from the Sheik's forearm.
Continuity mistake: When the baskets are being loaded to be lowered into the Valley of the Lepers, someone loads two heads of lettuce onto a basket. Just as the basket is being lowered, someone else throws in three more heads. When the basket hits the bottom, there are only three heads of lettuce.
Factual error: In the movie, Pontius Pilate is appointed to be governor of Judea around AD 32 (Judah is enslaved in AD 28, spends 3 years as a slave and then at least one year with Arrius before he meets Pilate, who is still not appointed). In reality, Pilate was the governor of Judea from AD 26-36.
Revealing mistake: When Judah and Messala hurl their spears into the wooden beam, the projectiles follow very straight paths all the way across the room to their targets, whereas due to gravity they'd really travel curved paths, practically parabolic, requiring a skilled thrower to aim above the target. What's revealed here is that the spears were rigged to slide on thin wires, to assure that they'd hit the target on cue.
Continuity mistake: In the parade of chariots before the race, the riders are shown circling the track once before making their way to the starting line. As they emerge from the stables, the horses and chariots leave very noticeable tracks on the ground so you can trace their progress around the track. The riders head down the right side of the track (from the perspective of the stables) then make the wide turn to head down the backstretch, and then make the wide turn back onto the right side of the track where they started. The film then cuts to a wide shot of the riders heading back down the right side of the track for the second time, but the track ahead of them and all the way down the backstretch is now clean of any tracks. It's clear this shot comes from when the riders first emerged from the stables. The riders then stop on the starting line on the backstretch, which means they were either transported to the other side of the track without making a third turn, or they did 1 lap around the track in the space of 1 and a half laps.
Factual error: Emperor Tiberius of Rome was a reclusive and vicious tyrant by 26AD when "Ben Hur" is set. Furthermore, by that time, he had retired to Capri and was rarely in Rome. In the movie, he's the picture of Regal benevolence, basking in the love of the crowds and showering glory on Arrias in victory. In real-life that never would have happened. Tiberius' Governor Sejanus would have presided over Arrias' triumph, not Tiberius.