Simplify the following text for a Grade 11 native English-speaking person.
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 .