Revealing: When Alexander is about to wake up at the end of his journey from 2037 to 802,701, it cuts to a shot of the year display counter on his machine. The 100,000's digit is spinning just as fast as the 1's digit and all the others, rolling over several times without the millions digit moving. If the counter was moving correctly, as it is in all other shots of it, then the 100,000's digit should be moving slowly, or the millions digit should also be moving.

Continuity: After the final fight is over, most of the blood on Alexander's face, and especially the blood in his mouth, disappears.

Revealing: During Alexander's long journey, it shows an elaborate geological sequence. It shows the area turning to desert and then trees and plants begin to grow. If you look at the background, trees grow up, then shrink in the same manner instead of dying and falling over. The special effects crew just reversed the growing sequence.

Factual error: In the middle of the movie, when Alexander is traveling through time and the landscape around him is evolving, the geologic sequence makes no sense. It shows sand and dust covering what was once New York, then water forming into a river and wearing down the gorge, and then a glacier covering the area. The glacier would have exerted hundreds of millions of tons of pressure on the land, smoothing out the gorge that had worn down through the sedimentary rock. The glacier would then have melted into the hollow it had formed, much like the Great Lakes. It would have made more sense for the glacier to have come first, then retreated and melted to form a river that carved out the gorge.