The allusion in this passage primarily comes from “the ides of March.” This phrase refers to a specific date in the Roman calendar, March 15, which is famously known as the date of the assassination of Julius Caesar in 44 BCE. In the context of the passage, Brutus is invoking this date as a reminder of the moral and ethical implications surrounding Caesar's death and the reasons behind it, specifically the theme of justice.
While the other phrases have their own significance—"supporting robbers" refers to the conspirators’ claim that they acted against tyranny rather than for personal gain, “be a dog and bay the moon” expresses Brutus's disdain for those who would dishonor themselves for monetary gain, and "foremost man of all this world" refers to Julius Caesar’s status as a powerful leader—they do not carry the same historical and thematic weight as “the ides of March” in this particular context.