Roman Emperor Augustus is made Pontifex Maximus, the high priest of the College of Pontiffs in Rome.
The most important office in the religion of ancient Rome, it now becomes subsumed within the role of Roman Emperor. Thus the highest political office and highest religious office are now one and the same.
Much later, "pontifex" will be used as a title for Christian bishops and Pontifex Maximus becomes a title for the pope, the bishop of Rome. Technically, though, Pontifex Maximus is not an official title for the pope.