A mara or mare is a kind of malignant female wraith in Scandinavian folklore believed to cause nightmares. She appears as early as in the Norse Ynglinga saga, but the belief itself is probably even older (see below). "Mara" is the Old Norse, Swedish and Icelandic name, "mare" is Norwegian and Danish.
The mara was thought of as an immaterial being capable of moving through a keyhole or the opening under a door who seated herself at the chest of a sleeping person and "rode" him or her, thus causing nightmares. In Norwegian/Danish, the word for nightmare is mareritt/mareridt, meaning "mareride". The Icelandic word martröð has the same meaning, whereas the Swedish mardröm translates as "maredream". The weight of the mara could also result in breathing difficulties or feeling of suffocation (an experience now known as sleep paralysis).
