The legend of Saint Erasmus
As a bolt of lightning strikes the ground near him, Erasmus continues his preaching. This is why he became the patron saint of sailors.
Thelatter, fearing the danger of storms at sea, decided to pray to him whenever the weather was bad. The electric discharges at the mastheads of ships were seen as a sign of his protection and were thus called "Saint Elmo's fires".
Saint Elme is the other name of Saint Erasmus.