The most prolific female murderer and the most prolific murderer of the western world, was Elizabeth Bathori, who practised vampirism on girls and young women. Throughout the 15th century, she is alleged to have killed more than 600 virgins in order to drink their blood and bathe in it, ostensibly to preserve her youth.  

She was a niece of Stephen Bathori, head of an eminent Hungarian family and Prince of Transylvania, who became king of Poland in 1575. Married to Count Nadasdy, she lived at Csej Castle in the Carpathian Mountains, in what is now Romania.  When her murderous career was discovered, the countess was walled up in her castle from 1610 until her death in 1614.