From Gladiator wiki
Colosseum
The Colosseum is the grand Flavian Amphitheatre in Rome, serving as the central stage for the brutal gladiatorial games that define the political and social life of the Roman Empire.
The Colosseum serves as the primary setting for the high-stakes combat that drives the Gladiator franchise. It is an architectural marvel designed to host elaborate public spectacles, ranging from re-enactments of historical battles to the lethal duels between trained gladiators. For the citizens and the elite of Rome, the arena is a place of entertainment and a tool for political manipulation, where the Emperor can sway public opinion through the display of violence.
Significance to Combat
For the protagonists, the Colosseum represents the ultimate proving ground where survival is the only currency. The arena floor is where personal vendettas and political conspiracies converge, forcing fighters to demonstrate both physical prowess and tactical intelligence to earn the favour of the crowd. Its status as a theatre of death ensures that every match carries the weight of life or death, making it the focal point for the themes of vengeance and redemption that permeate the series.