Priapus is a well-known Roman fertility god. After the Christianization of Europe, his worship was suppressed along with all the other pagan gods. But, while certain gods and goddesses could be subsumed relatively easily into Christianity (for example, the worship of Diana was a natural fit with the cult of the Virgin Mary, and Mithras could be merged into the Archangel Michael), Priapus was more difficult to blend into Christianity's anti-sexual system.
One of the most interesting and inconsistent elements of Christianity therefore is the existence of "phallic saints." These are saints who are associated with fertility and whose favour is thought to bestow sexual potency. Some of these are probably the remains of earlier Priapic cults that were only incorporated into the new religion with great difficulty and inconsistency.
Some notable examples include:
St. Cosmas and St. Damian at Isernia in Italy
St. Ters at Antwerp in Belgium
St. Foutin at Embrun in France
St. Guerlichon at Bourg-Dieu in France
St. Giles at Cotentin in France