Medieval architecture evolved from many of the
building forms and construction techniques that the
classical world developed before the Christian era.
In particular, the Romans had perfected arches, var-
ious forms of vaulting, intricate sequential layouts of
buildings, and a repertoire of symbolic architectural
forms. These provided the basis for plan, structure
and meaning adapted to Christian usage in the sim-
plest to the most complex medieval buildings
throughout the Middle Ages.

The simplest and oldest structural device is the post
and lintel system, where two upright posts support a
horizontal member, or lintel. It has been used since
time immemorial, in timber and in stone. Stonehenge
(ca. 2750-1500 B.C.), with its huge horizontal blocks
of granite placed upon even more massive rough-
hewn upright supports, exemplifies an early and mon-
umental form of this structural system. Colonnaded
peristyles in the Hypostyle Hall of the Temple of Amun
at Karnak in Egypt (ca. 1290 B.C.) and around the
Parthenon ( 447-438 B.C.) on the Acropolis in Athens,
provide more sophisticated examples of these forms.
But the post and lintel system has its limitations. The
length relative to the thickness and tensile strength of
the timber or stone lintel limits the possible span
between the columns, for if the supports are too far
apart the lintel will sag and then crack.

The perfection of the semicircular arch allowed a
greater span between posts, but required adequate
buttressing in the form of thick supports or addi-
tional flanking arches to counter the diagonal thrusts
generated by the accumulated wedge-shaped vous-
soirs that made it up ( fig. 1.1 ). The Romans perfect-
ed the arch and used it in the construction of mas-
sive aqueducts such as the Pont du Gard ( fig. 1.2 )
in Provence ( first century B.C.). Used decoratively,
such arches alternate with entablatures in the free-
standing peristyle around the reflecting pool of the
Canopus at Hadrian's Villa at Tivoli outside of
Rome (after A.D. 130; fig. 1.3 ).

When an arch is extended three-dimensionally it
forms a tunnel, or barrel vault ( fig. 1.1 ). The
Romans used this device in the Cloaca Maxima in
Rome, an underground sewer vaulted with brick
voussoirs, as early as 200 B.C. The surrounding earth
countered the outward forces while the wedge-
shaped voussoirs prevented internal collapse.
Aboveground, however, barrel vaults need massive
walls to absorb the outward thrusts generated by the
vault, although arched openings could penetrate the
wall and channel the forces above them into the
mass of the flanking structure.

The intersection of two barrel vaults at right
angles (one longitudinal and one transverse) forms a
groin vault ( fig. 1.1 ). The groin vault channels the
forces of the vault down onto the corner supports,

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