The origins of the title, which may literally be translated as ‘the greatest (maximus) bridge-builder / maker of bridges (pons facere)’ are obscure.
It may have initially been used as an acknowledgement of the importance of the man whose job it was to oversee the spanning of the sacred river Tiber, or it may have been intended to convey a more symbolic role, an official whose job it was to act as a bridge between the human world and that of the gods.
The chief priest had many important duties, including the overseeing of the state calendar, the regulation of marriage and the supervision of public morals. According to Roman legend, the first Pontifex maximus was Numa Marcius, appointed by Numa Pompilius, the second king of Rome, in around 700 BC. Augustus, the first emperor, took control of the priesthood in 13 BC, the title becoming one of many used by successive heads of the Roman State, Pope Leo I acquiring it in the mid 5th century.
Today the term ‘Pontiff’ is used to describe any bishop, the Pope having the official title of ‘Supreme Pontiff of the whole Church’ (Summus Pontifex Ecclesiae Universalis).