Decimus Aelius Meridius Maximus?
The protagonist (played by Russell Crowe) is often called "Maximus". I've tried to figure out his full name based on some clues in the film. I'm posting here with the hope that someone can illuminate the issue while avoiding idle speculation. In the paragraphs below, I present my conclusion (as though it was authoritative), and I follow that with supporting evidence. I welcome -- No, require! -- comment (but of course, only if you enjoy such stuff -- otherwise, just enjoy the show).
About the protagonist's name: The film's protagonist (nonsensically) calls himself "Maximus Decimus Meridius" and is later (doubtfully) announced as "Aelius Maximus". The first case is nonsense because "Maximus" is an honorific (an agnomen) which one would hardly apply to themselves and because a recognized clan name (a nomen gentilicium, or simply nomen) is missing. The second case, though not impossible, is doubtful because appending the "Maximus" agnomen to the "Aelius" clan name (literally: "the highest of the Aelii") would leave the protagonist's identity quite mysterious (and would also be quite misleading since the "the highest of the Aelii" would undoubtedly be taken to refer to emperor Hadrian, a man who could hardly make an appearance since he'd been dead for 2 generations). Though the nomenclatures in the film are wrong, they provide the necessary name parts to figure out the protagonist's proper, full name: "Decimus Aelius Meridius Maximus". In official functions he would be announced by his full name (with the "Maximus" honorific when appropriate), but in casual conversation he would be called "Decimus" or "Maximus". In informal 3rd person he would be referred to by "Aelius Meridius" or simply by "Meridius" (or very informally, by "Decimus", as I refer to him, below).
About Latin names: Latin names took the form: praenomen nomen cognomen agnomen agnomen etc. (i.e., personal name + clan name + family within the clan + honorifics -- see Wikipedia "Roman naming conventions"). For example, "Gaius Julius Caesar" is literally "Gaius of the Julii in the house of Caesar". The source of the family name "Julius Caesar" is likely this: In earlier Roman history there was a notable person, Caesar Julius (literally: "Caesar of the Julii"). His descendants wished to advertise their link to him and to delineate that lineage from that of other Julii, so they called themselves Julii Caesars. Thus, "Julius Caesar" became the family name (i.e., the nomen + cognomen) of the descendants of Caesar Julius. Put another way, "Julius Caesar" popularly refers to Gaius Julius Caesar in the same way that "Einstein" popularly refers to Albert Einstein.
About the protagonist's cognomen: "Meridius" (literally: "from the South" -- Hispania Baetica is in southern Spain) is undocumented but it must be a (probably fictitious) cognomen. The protagonist has to have a cognomen and, based on futher nomenclature resolution (below), "Meridius" is the only candidate. So by process of elimination, "Meridius" must have been his cognomen.
About the protagonist's nomen: "Aelius" (literally: "of the Aelii") is the documented clan name of an illustrious patrician clan dating from Rome's founding. A person's nomen preceeds their cognomen, hence: Aelius Meridius. The Aelii were the clan that produced a long list of consuls (the highest public office) which included emperor Hadrian.
About the protagonist's praenomen: "Decimus" (literally: "10th") is a documented praenomen probably meaning that he is 10th generation head of the Aelius Meridius family. A person's praenomen preceeds their nomen, hence: "Decimus Aelius Meridius".
About the protagonist's agnomen: Maximus (literally: "the highest") is a documented agnomen. If a person has a agnomen, it follows their cognomen, hence: "Decimus Aelius Meridius Maximus" completes the protagonist's full name.
About the protagonist's lineage: The nomen Aelius implies that emperor Hadrian (born Publius Aelius Hadrianus), who was also from Hispania Baetica, was Decimus's great grand-uncle. Decimus therefore was the 4th cousin once removed of emperor Marcus Aurelius (played by Richard Harris), which makes him the 5th cousin of Commodus (the film's antagonist, played by Joaquin Phoenix).
About the protagonist's dilemma: Marcus Aurelius wished to adopt Decimus as his son. The implication is that Marcus intended to designate Decimus to be the next emperor, so to carry on the tradition of the preceeding string of "Five Good Emperors" who had bypassed their biological sons by choosing successors based on merit. Roman law allowed this. Marcus Aurelius himself had been adopted by the prior emperor: Antoninus Pius, who had been adopted by the prior emporer: Hadrian, who had been adopted by the prior emperor: Trajan, who had been adopted by the prior emperor: Nerva. But with Marcus's death, his biological son, Commodus, became emperor -- this is entirely fictional since, in reality, Marcus made Commodus co-emperor 3 years earlier (but this story diverges from history in that regard).
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