Denis’s Legend says he was sent by Pope Fabian to Gaul with several other missionaries. (Fabian was pope from A.D. 236—250.) Denis was appointed the first Bishop of Paris, but he was arrested, imprisoned, and then executed by the Roman Governor. (Persecution of Christians was common under then-Emperor Decius.) Denis was executed along with two companions, a priest and a deacon, who later were assigned the names Rusticus and Eleutherius, respectively. According to tradition, they were executed on Montmartre, the highest hill in Paris, whose name possibly derives from this event (Mons Martyrum, “the Martyrs’ Mountain”), although the name may predate the saint’s death (it could also be Mons Mercurii et Mons Martis, “Hill of Mercury and Mars”).
The Legend continues that Denis then picked up his own head, and walked several miles, preaching a sermon all the while. The place where he actually died was marked by a small shrine, later the site of the Basilica of Saint-Denis, which became the traditional burial site for French royalty. Denis was the original patron saint of the French people (he was eclipsed later by Joan of Arc), and he is honoured as one of the Fourteen Holy Helpers, a group of saints venerated starting in the 14th century for their protection against the Black Death and other illnesses. Denis was specifically invoked against diabolical possession and headaches.
Denis’s feast day is 9 October.