Crypt Of The So-Called Oracle Of The Dead At Ephyra, in western Greece (third century B.C.). It is typical of Greek architecture
that the vault is used in an underground structure. The principle of the arch and vault was known to Democritus in the fifth century
BC. but surviving examples date to the second half of the fourth century or later.
New structural forms and techniques did not make enormous headway east of the Adriatic. Post-and-lintel construction remained the
basis of architectural form, and dressed stone, timber, and mud brick the staple constructive materials. In the time of Alexander,
however, perhaps as a result of experience gained by his engineers in the East, vaults and arches became more common in the Greek
world. Vaults were used to span the tomb-chambers of Macedonian nobles, and isolated examples are found in later buildings,
generally in an inconspicuous or subordinate role. Sloping vaults covered the narrow passages leading to the interior court of the
temple at Didyma, and barrel-vaults met at right angles in various Pergamene buildings. Elsewhere arches were used in subterranean
structures to support stone paving above or (in the crypt of the third-century Nekro-manteion at Ephyra) to bear the weight of a
barrel-vault. In all cases the construction was carried out in stone, even though this might lead to structural weakness, especially
where vaults intersected. The octagonal Tower of the Winds in Athens, an elaborate water-clock and planetarium built by
Andronicus of Cyrrhus in the mid first century B.C., was roofed by a series of long wedge-shaped blocks bearing upon a central
keystone. Only with the development of concrete construction in Italy (below, pp. 516 ff.) did vaulting become a fundamental
component of architecture, destined to open up undreamt-of possibilities in the expansion and manipulation of interior space.
One final general aspect of Hellenistic architecture is the composition of ensembles which were visually unified, whether by the use
of recurrent motifs or by the setting of one building as a foil to another. The urban foundations which Alexander and his successors
planted in the newly conquered areas were a good testing ground for the planners. Most of them were laid out in accordance with the
traditional Hippodamian, rectilinear grid, and, though development could be piecemeal and incoherent, as it had often been in the
past, there was increasing concern to relate buildings to one another and to frame and define space by means of the ubiquitous stoa.
The best-known examples are the monumental piazzas of Miletus and Priene, both pre-Hellenistic chequerboard cities which
experienced major programmes of building during the third and second centuries B.C. Even the chaotic sprawl of the agora in
Athens had some order imposed upon it at this time with the construction, at right angles to each other, of the Middle Stoa along the
south side and the Stoa of Attalus on the east. In another pre-Hellenistic city, Rhodes, unknown planners stacked buildings on the
acropolis in a masterful exercise in giving architectonic shape to a sloping terrain. It was from beginnings such as these that the great
terraced complexes at Lindus and Cos, with their broadly axial layouts and monumental stairways, evolved. But the finest