succeed each other from east to west. One meridian was taken
to run down the Nile, and through the Cilician Gates and
Sinope to the mouth of the Ister (Danube). Since these lines
were far from 'straight', the distortion introduced into the
map was considerable. In this way also an east-west axis for
the Mediterranean was established; since, in coasting along
considerable stretches, the west coast of Italy and the south
coast of France, for example, the change in direction was gradual
and not easily perceptible, these portions tended to be shown
as parallel to the east-west axis. The Mediterranean was thus
narrowed in proportion to its length. A general principle which
governed much Greek thinking then entered into the delinea-
tion of the map--namely, the symmetry of nature. Features
north of the axis must be balanced by similar features to the
south; the Pyrenees by the Atlas mountains, the Adriatic by
the Gulf of Syrtes, Greece by the Cyrenaica promontory, and
so forth. This principle was applied further afield; the Nile
being thought to flow in its upper course from west to east, the
unknown upper course of the Ister was made to do likewise.
Emphasis on this point is necessary, for it strongly influenced
later ideas on the earth's configuration. Ptolemy probably
conceived his enclosed Indian Ocean as a counterpart of the
Mediterranean. The frame of the world map continued to be
circular, and, for the Greeks, centred at Delphi--assumptions
which the philosophers often derided.

Meanwhile the progress of science was revolutionizing
conceptions of the earth, and suggesting much more precise
methods of fixing position on its surface. The idea that the
earth was a sphere, and not a flat disc, was first advanced by
philosophers of Pythagoras' school, and brought to general
attention through the writings of Plato. When the spherical
character of the earth was recognized, and later the obliquity
of the ecliptic, astronomers were able to deduce latitudes from
the proportions between the lengths of the shadow and the
pointer of the sun dial. This was the forerunner of the modern
method of obtaining latitude by observing the altitude of the
sun at midday and applying the necessary correction from
tables in the Nautical Almanac.

Thus alongside the 'mapping' of relatively small areas for

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