Faerie Dwellings
Doorways
The threshold of a house is an uncertain place, neither inside or outside, but a boundary between the two. When a person crosses a threshold he or she moves from one state to another and may be in danger from the spirits that dwell between, as many spirits do. In many cases, it was thought unlucky to tread on the threshold itself, and people were always careful to over it...not on it. This is why brides, in a transitional stage of life, are carried across it.
A number of faeries live beneath thresholds, including the French Follets (who are ill-tempered, but will act as house faeries if you win their respect) and the Russian house faery, the Deduska Domovoy. Because not all faeries are kind or welcome, the Irish scattered primroses on the doorsteps to keep them from crossing it, and in England thresholds were made of protective holly wood for the same reason. In parts of Britain, defensive designs called "step patterns" were drawn on the doorstep in salt or chalk, or reproduced in mosaic. These took the form of knot work and "tangled thread" patterns because faeries like to follow straight paths when traveling...they tend to get caught up in trying to follow the twisted lines.