Commodus could have killed him in his cell
Like, almost at the beginning so why did this last 2 hours again?
shareCommodus had a public relations problem and inferiority complex. He wanted the "mob" i.e. the citizens of Rome to love him unrequitedly, which they did not. That was the initial reason he killed his father and and ordered Maximus executed, whom he knew were loved more than he.
Commodus thought Maximus was dead up until the first arena fight, however, unknown to him
Maximus had built up a reputation as "The Spaniard" via his arena wins in the provinces and the people of Rome wanted to see him in action. (If you remember Lucius, Lucilla's son, asked Maximus in his cell if he was The Spaniard, in addition to liking him)
When Maximus removed his helmet to reveal he was alive after the first arena fight, he at that point had won the favor of the "mob" who wanted him spared. In addition, Lucius had come out into the arena with Commodus, who knew that executing Maximus in front of everyone would not only make him look evil and merciless in front the "mob", but also in front of his sister's son.
Not a good way to get people to love you.
So he needed Maximus to die in combat in the arena, first he brought back the popular Tigris to defeat Maximus, which failed, then he decided to try and defeat Maximus in the arena himself...thus proving himself and winning back the mob. Of course, it was all setup for him to win but Maximus still killed him.
So in the final analysis Commodus had to find a way to kill Maximus other than executing him.
Not true, if he had killed him in the dark nobody would have noticed.
shareRemember Maximus was the featured attraction, the crowd knew about him as The Spaniard before he went into the arena, but Commodus didn't know it was Maximus. So he wouldn't have killed him prior.
In the arena, Maximus then won the crowd...that was the key to removing Commodus from power, to win over popular opinion. The crowd wanted him spared so Commodus gave the thumbs up because he knew if he didn't then popular opinion would turn against him.
Now to your point...If Commodus had killed him covertly, certainly the crowd would wonder what happened to him and word of his execution would've spread. As would the senators wonder. So his hands were tied. He needed Maximus alive to die in the arena and ultimately by Commodus' hand in the arena so he could win back the crowd.