According to Millar, what power did the Roman people have?

Democratic power.

Explanation:

Greek's system was really advanced in subjects as government, democracy, freedom, republics, freedom of speech ...

One example of that are the assemblies that they maintained in the Agora to discuss important matters for the nation, there were able to participate every citizen.

According to Millar, he said that there was 3 formal powers: 1.) residual role of the assembly to meet as criminal courts 2.) elections conducted by eather the Century Assembly or the Tribal Assembly 3.) able to legislate