. The Sassanide monuments bear
witness that many centuries after the destruction of Nineveh the custom of
placing cylinders of terra-cotta in vaults was still practised. In spite of
its small scale these circles may be distinguished in the woodcut of the
Sarbistan palace which we have borrowed from Coste and Flandin (Fig.
54).[226]

These same writers have ascertained that the architects of Chosroes and
Noushirwan employed still another method of lighting the rooms over which
they built their domes. They gave the latter what is called an "eye," about
three feet in diameter, through which the daylight could fall vertically
into the room beneath. This is the principle upon which the Pantheon of
Agrippa is lighted; the only difference being one of proportion. In
Persia, the diameter of the eye was always very small compared to that of
the dome. If we are justified in our belief that the constructors of the
Parthian and Sassanide palaces were no more than the perpetuators of
systems invented by the architects of Nineveh and Babylon, the Assyrian
domes also may very well have been opened at the summit in this fashion. In
the bas-relief reproduced in our Fig. 42, the two small cupolas are
surmounted with caps around a circular opening which must have admitted the
light. Moreover, the elaborate system of drainage with which the
substructure of an Assyrian palace was honeycombed would allow any rain
water to run off as fast as such a hole would admit it.[227]

Whatever may be thought of these conjectures, it is certain that the
architects of Nineveh--while they did not neglect accessory sources of
illumination--counted chiefly upon the doors to give their buildings a
sufficient supply of light and air. As M. Place says, when we examine the
plans of Sargon's palace at Khorsabad we are as much astonished at the size
of the doorways as at the thickness of the walls.[228]

"There is not a single doorway, even of the smallest chambers, even of the
simple ante-rooms for the use of servants and guards, that is not at least
six feet or more wide; most of them are ten feet, and those decorated with
sculptures even wider still." In their present ruinous state, it is more
difficult to say for certain what their height may have been. Judging,
however, from the ruins and from the usual proportions of height and width
in the voids of Assyrian buildings, the doors at Khorsabad must have risen
to a height of between fifteen and twenty-two fee