Denis (Dionysius) was sent from Italy by Pope Fabian around 250 as one of seven missionary bishops to the still-pagan Gauls. He established his see at the village of Lutetia — the future Paris — together with his companions the priest Rusticus and the deacon Eleutherius. Their preaching converted enough of the population that the Roman authorities arrested them.
Decapitated together at Montmartre ('mountain of the martyr'), Denis — according to the famous tradition preserved in the Golden Legend — picked up his severed head and walked six miles north, preaching all the way, before collapsing on the spot where the great Basilica of Saint-Denis was later built. The motif of saints carrying their own heads ('cephalophory') was named after him.
The Basilica of Saint-Denis, on the site of his collapse, was built starting under Charlemagne and rebuilt by Abbot Suger in the 12th century as the first Gothic building in the world. It became the burial place of every King of France from Dagobert I (639) to Louis XVIII (1824) — the royal necropolis of medieval and early modern France. Denis is the principal patron saint of France.