Final answer:
Flavius and Marullus are on the streets to scold and disperse the citizens celebrating Caesar's victory and to remove decorations honoring Caesar.
Step-by-step explanation:
The main purpose of Flavius and Marullus, who are characters in Shakespeare’s play Julius Caesar, being on the streets is to confront and disperse the commoners celebrating Caesar’s triumph over Pompey. They are troubled by the fickleness of the public, who not long ago cheered for Pompey but now celebrate his defeat.
The tribunes criticize the citizens for their disloyalty and order them to leave, subsequently taking down decorations meant for Caesar in an attempt to diminish the pomp of his return to Rome.