The word for today is – IMPERIUM – meaning – power. The Romans pointed out the difference between IMPERIUM and AUCTORITAS. Some leaders ruled by AUCTORITAS – meaning – AUTHORITY, without resorting to power.
Augustus (died A.D. 14), the first Roman emperor who ordered a census taken in his empire ruled primarily with authority. Sometime around 17 B.C. a judicial change was made. Under the Republic, any citizen found guilty had the right to appeal to the people. However, Augustus was given the authority to overturn a sentence of death by his use of his IMPERIUM.
So PROVOCATIO AD POPULUM (an appeal to the people) gave way to APPELLATIO AD CAESAREM (an appeal to Caesar).
Hence, today we have the PRESIDENTIAL PARDON.