But some [beings], who live int he hills close to men, are more amicable and not so dangerous unless they chance to have been harmed by some kind of injury and provoked into wickedness. They seem, indeed, to be endowed with bodies of incredibly subtlety, since they are even thought to enter into mountains and hills. They are invisible to us unless they wish to appear of their own volition, yet the properties of certain men’s eyes are such that the presence of no spirit can ever escape their sight (as was Lynceus’s unhappy situation). They know a thousand devices and an infinite number of tricks with which they harass men in wretched ways, but their young people are said to have a similar stature, clothing, and even way of life to that of their human neighbors, and to take excessive pleasure in coupling with humans. Examples are not lacking of a number of the rogues who are said to have impregnated women beneath the earth and had access to them at fixed times or as many times as they wished. And from time to time the women of our land have been oppressed by these earth-dwellers and innocent boys and girls and the young people and adolescents of both sexes have very often been taken away, though quite a few are restored safe and sound after a number of days, or sometimes a number of weeks, but some are never seen again, and certain ones are found half-alive, etc.Oddur Einarsson, bishop of Skálholt, translated by Richard Firth Green in “Elf Queens and Holy Friars” pp. 13-14.
That quote comes from the first collector of Icelandic manuscripts, in a geographical treatise describing Iceland, written in the late 1500’s. I quote it here because it offers a terrific snapshot of the tenacity with which beliefs in elves (landvaettir in Iceland, of course) held the imagination of the people centuries after the conversion to Christianity.
It’s worth noting that the quote goes on to say how similar beliefs have hold all over Europe; this isn’t an Icelandic phenomenon. But what I love is the fact that it shows a continuity in folk-belief between the pre-Christian beliefs in land-spirits and 16th century (and even modern!) beliefs in elves.
At some point the Alfar of Norse mythology got superimposed upon the landvaettir, which is definitely something that points to some sort of overlap between their relative cults, and also brings Freyr (as lord of Alfheim) into the mix, but for now the continuity expressed by that passage is impressive enough to my mind.