Original: The toponym Mons Martis ("Mount of Mars") survived into Merovingian times, Christianised as Montmartre, signifying 'mountain of the martyr'; it owes this name to the martyrdom of Saint Denis, who was decapitated on the hill around 250 AD.
Simplified: Montmartre means' mountain of the martyr '; it owes its name to the martyrdom of Saint Denis, who was decapitated on the hill around 250 AD.