Great question — answering as the UphillTech team:
There is no answer which can be confirmed or denied in official capacity, but the "reality" is along the lines of "how else can you effectively stage a coup in an era where there is only verbal or written communication when no one can be trusted not to be in the emperor's pocket, other than having the principal players meet and build trust in person?" Gracchus invokes that his presence is evidence Maximus can trust him and his voice is the voice of the senate. Maximus suggests that if he is freed and can reach his army in Ostia, they can return to take Rome. Gracchus is leery of trading one dictatorship for another. Maximus confides he will return Rome to the senate as it was the dying wish...
Full answer by shigginpit: https://movies.stackexchange.com/a/119146 (CC BY-SA 4.0).
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