When speaking to his troops at the riverside in India, Alexander's sword switches from the left to his right side in one shot.
In the theatrical version of the movie, the scar on Old Ptolemy's forehead switches sides halfway through his first scene.
Antigonus addresses his troops just before the jungle battle against the Indians. In a flipped shot, his right eye is missing, not his left.
When Alexander is riding towards the warrior on the elephant, the arrows in his horse's shoulder blades disappear and reappear between cuts to Alexander and the elephant.
When Alexander tries to ride the wild black horse, the ropes are crossed. In the next shot, they are in place.
When Alexander asks Darius' daughter how she wishes to be treated, she replies, "like a princess," and he grants her wish. In reality, Alexander asked the question to the Indian king Porus. When Porus replied, "like a king", he won Alexander's respect and became one of his allies.
When Alexander and his fellow Macedonians are children, they all look to be around the same age. However, Nearchus was four years older than Alexander, Ptolemy was eleven years older, Antigonus was 26 years older, and Philotas was nine years younger.
On the map of the known world, the Black Sea is correctly called "Pontos Euxeinos," but the Mediterranean is called "Mare Mediterraneum." On Roman maps, it was called "Mare Nostrum" (Our Sea) or "Mare Internum" (Inner Sea). In the fifth century BC, Herodotos called it the "Pontos Boreios" (Northern Sea).
On road marches (as opposed to marching to contact, i.e., when the enemy is in sight or there is imminent contact), the 4 to 7 metre (13 to 21 feet) sarissa would have been broken down into its two components for ease of transport. In the movie, the sarissa is always shown at full-length deployment.
In the battle at Gaugeamela, the Persian army is wearing dark clothes. Their uniforms were yellow and light purple.
When it comes to naming an heir to Alexander's empire on his deathbed, no mention is made of Alexander's half-brother, Philip Arrhidaeus. Despite his noted learning disability, Arrhidaeus was held up as the true Macedonian heir to Alexander's empire by many men in the Macedonian army. (Alexander's child by Roxane was still unborn before Alexander died and was also half-Iranian, which fueled Hellenic prejudices.) Arrhidaeus was crowned Philip III after Alexander's death as co-ruler alongside Alexander's unborn child (who became Alexander IV). While some have called the film out on this factual error, the omission was clearly done to compress the story of Alexander into a single film.
When Olympias is telling Alexander that Zeus is his father, she says "I laid with him that night", but her mouth isn't moving. This is, however, a dramatic flourish which Oliver Stone is known to do.
[Director's Final Cut] At Philip's wedding, when Attalus is toasting a Macedonian Queen to be proud of, he pauses to glare at Alexander but as he does so, his dialog continues without moving his mouth. This, however, is an intentional artistic flourish that is typical of Oliver Stone's films.
The tattoo on Colin Farrell's right arm and shoulder appears in a few shots.
When Alexander rides towards the elephant of the Indian King, his sword is obviously waggling as though made of rubber.
Many scenes were reordered in the "Final Cut." For example, Alexander's childhood is seen in flashback, not at the beginning in chronological order. However, the end credits are the same, so the list of actors "in order of appearance" is inaccurate.
Ptolemy I is depicted recounting the story of Alexander in 283 B.C. The Lighthouse at Alexandria, seen in the background, was built during the reign of his son Ptolemy II, around 270 B.C.
In Gaugamela Battle, we can clearly hear that the Persian army leaders are talking Arabic. But this battle was before Arabs invasion to Persia so there weren't Arabic words in Persian.
The horse used as Bucephalus is a modern Dutch Friesian, the 1990's Hollywood dream horse (Zorro, Ladyhawk etc etc), and about twice the size of the ponies known in the Hellenistic period.
The Alexander Mosaic shown when the old Ptolemy was talking did not exist until 100 BC. It was from the Roman Republic era.
Knick knacks in Olympias' boudoir include the Sumerian Goat and Tree excavated at Ur, in modern day Iraq, by Leonard Woolley in 1927. Created and buried more than 2000 years before Alexander was born, it's unlikely his Mum had one on her sideboard.
When Aristotle is describing what he thinks might be a route to circle around to the headwaters of the Nile and travel down it to conquer Egypt, he refers to going "up the Nile," rather than down it. This may be due to the modern map convention of showing North at the top of maps and referring to traveling in a northerly direction as going "up". The Nile River flows from South to North and thus traveling down the river is going North.
They talk about Hindu Kush in the movie. The first reference to this name shows up more than 1300 years later.