Seats in the choir, wholly or partly enclosed on the back and sides, mentioned from the 11th century.
In the earlier period the subsellia of the clergy were placed in the apse on each side of the bishop.
Formae, seats with backs, and stalli, connected seats, were introduced.
They became fixed and were ornamented with carving.
In the Gothic period the architectural effect was sometimes exaggerated.
There was beauty in the rich carving of the front and rear faces and on the misericordia under the seat which was often carved with grotesque designs.
Few changes have been made in the form in modern times.
New Catholic Dictionary