The Elizabethan stage was quite different from the modern one. Many plays were performed by traveling companies, often in ad hoc performance spaces such as inns and churches. Even when permanent spaces such as the Globe Theatre were first built for theatrical performances, such spaces retained the minimalistic air of their predecessors.
Because the stage was surrounded by spectators on three sides, and there was no way to block the stage off from view during scene changes, only a limited amount of props and stage furnishings could be used. This meant that the effects of Julius Caesar had to be created either by the language of the play itself or by smaller props and costumes.
Costumes tended to be especially dramatic and colorful, giving visual interest to the stage, and thus serving to compensate for the lack of scenery. The large cast of extras and bit actors in the plays made costume an especially important visual element.