The historical accuracy of gladiator in some aspects was quite good but in others, quite bad. Even right from the opening scene, the inaccuracies start. First, there was no last great battle with the Germanic tribes on the eve of Marcus Aurelius' death. There was a great daylong battle late in the campaigning season of A.D. 179, but Marcus died on March 17 of 180, just as he was about to launch another great military campaign. It is most probable that the scriptwriters needed to shorten the chronology here to save time in a long movie, but that wasn't their only mistake relating to battles. The use of fire-hurling catapults and mechanical dart launchers against the oncoming barbarians was certainly dramatic but probably unhistorical. Such weapons were too burdensome for use on the open battlefield, thus were confined to more static siege warfare.
I have found no proof corresponding to the Roman commander Maximus, the movie's hero, and if there were one, it would not have been a German shepherd, a breed that did not exist in ancient times.
Marcus Aurelius was not quite 59 when he died, perhaps of plague. "Gladiator" does capture his kindly and philosophical nature, but his decrepit frailty, thin beard, and wispy fly-away hair in the movie bear little resemblance to his statues and portraits on coins. They show him as a fairly vigorous man with a full beard and a thick head of curly hair.
The whole movie in addition radically compresses the chronology of the Emperor Commodus' reign. He became sole emperor upon his father's death in March of 180AD and was assassinated almost thirteen years later on December 31, 192AD. Although the time covered by "Gladiator" is not precisely indicated, it would appear that no more than two years could...