   The second half of the 5th century B.C. was the Golden Age of
Greece. This was the period of her most beautiful art and
architecture, and some of her wisest thinkers besides. Both owed
much to the popular new study of geometry.  By the start of the
next century, geometry itself was entering its own classic age
with a series of great developments, including the Golden Mean.
The times were glorious in many ways. The Persian invaders had
been driven out of Hellas forever, and Pericles was rebuilding
Athens into the most beautiful city in the world. At his
invitation, Greek mathematicians from elsewhere flocked into the
new capital. From Ionia came Anaxa- goras, nicknamed "the mind."
From southern Italy and Sicily came learned Pythagoreans and the
noted Zeno of Elea. And their influence was felt over all
Athens.    Elsewhere in the city, the impact of the new geometry
took another form. On the narrow streets of Athens walked world-
famous philosophers, talking to the people, lecturing on
mathematics, geography,