As the play opens, the citizens of Rome have taken to the streets to celebrate Caesar's triumphant return to Rome after defeating Pompey's sons in Spain. (Pompey had previously ruled in Rome.) Their mood is one of festivity and rejoicing as they enjoy a holiday from work. As the scene develops, Shakespeare presents these common people as being fickle in their loyalty to their leaders and easily swayed politically. Marullus, a Roman tribune, feels disgusted by their behavior and castigates them for their disloyalty, reminding them how they had once cheered for Pompey:
Many a time and oft
Have you climbed up to walls and battlements,
To towers and windows, yea, to chimney tops,
Your infants in your arms, and there have sat
The livelong day with patient expectation
To see great Pompey pass the streets of Rome
Marullus tries to drive them from the streets, telling them a plague would surely descend on them for their great ingratitude. This theme, that the common people are politically disloyal and easily influenced, is emphasized in Act III when Antony turns the crowd against the conspirators by manipulating the crowd with his emotional oration.
The fact that Marullus, as well as Flavius (another tribune), feels such anger at the crowd's behavior indicates that not everyone in Rome is pleased with Caesar's rise to power. Brutus' conversation with Cassius, which follows quickly in the plot sequence, makes clear the political division in Rome.