Door-posts

The Jews were commanded to write the divine name on the posts
(mezuzoth') of their doors (Deut. 6:9). The Jews,
misunderstanding this injunction, adopted the custom of writing
on a slip of parchment these verses (Deut. 6:4-9, and 11:13-21),
which they enclosed in a reed or cylinder and fixed on the
right-hand door-post of every room in the house.