f having the more constructive horizontal joint
used in the West.

The doors made of wood or of wood lined with bronze, swing on top and
bottom pivots which turned in bronze-lined sockets in lintel and
threshold. They closed with a rebate in the jambs and against the raised
threshold. Windows were sometimes filled in a similar manner, as in the
palace of the Porphyrogenitus and in the north gallery of S. Saviour in
the Chora (Fig. 100). In the latter double windows or shutters were
employed, opening inwards in the same way as did the doors. These
shutters may perhaps be regarded as domestic, for in the churches, as is
still seen in S. Sophia though the arrangement has vanished elsewhere,
the entire arched opening was usually filled in with a pierced marble
grille.

In addition to the simple round-headed windows double and triple windows
are found. Double windows were naturally formed by dividing the single
arch by a central pier. This method presented two varieties: either the
pier was continued up to the containing arch, thus giving two pointed
lights, or the two lights were covered by separate arches within the
main arch. Both methods are used in the narthex of S. Theodore (p. 247).
Another variety was produced by placing two single lights together, with
a shaft between them instead of the central pier. But as double windows
are not very satisfactory, triple windows are more common. In this case
both the methods just described of forming the windows were adopted. A
large semicircular opening divided by two piers will give an arched
light between two pointed lights, or three arched lights, as in the
narthex of S. Theodore. In the former case, if shafts are substituted
for the piers, a little adjustment will produce the beautiful form found
in the side-chapels of the Pammakaristos (p. 152), and of S. Saviour in
the Chora (p. 310), where the two side lights are covered by half-arches
whose crowns abut on the capitals of the shafts, while between and above
them rises the semicircular head of the central light.

The method of grouping three arched windows of the same height is
adopted in apse windows, each of them occupying one side of the
exterior. As the deep, narrow mullions are set radiating, the arch is
narrower inside than outside. But this difficulty was overcome, partly
by lowering the inner crowns, so that the arch is conical, partly by
winding the surface. In the Pantokrator (p. 238), instead of radiating
to t