As a tidal wave bears down on Pompeii, Atticus manages to save both a mother and her daughter by outrunning said wave. Seeing the two embrace after managing to escape is probably the film's most emotional moment.
Milo and Atticus going from callously plotting how to kill each other in the arena to fighting together and calling each other "brother".
Atticus dying a free man.
After retrieving Cassia from the villa, Milo reuniting with Atticus in the streets. He literally ran into his arms.