The ending, in which Maximus fulfills his vengeance as he dies, simultaneously restoring Rome to the republic that the true, dying Emperor had hoped for. He passes on to be reunited with his wife and son, and his fellow gladiators are freed. Of course, he's undoubtedly a legendary hero of Rome at this point, a paragon for all Romans to aspire to.
"Now we are free. I will see you again... But not yet. Not yet..."