It is maintained that the Milesian cosmology was based on the
primitive and popular theory of 'the four elements'. However, the
scientific conception of an 'element' did not exist at this date. We
shall see later that this was due to Empedocles, and it is only the
place that the old quaternion of Fire, Air, Earth, and Water occupied in
his system (and afterwards in that of Aristotle) that has led to these
being called 'the four elements'. It is an unfortunate confusion, but it
is very difficult to avoid it, and we must continue to use the word
'element' in two senses which have very little to do with one another.
The spirit of Ionian civilization had been thoroughly secular, and this
was one of the causes that favored the rise of science. The Milesian
school came to an end with the fall of Miletus in 494 BC, but 'The
Philosophy of Anaximenes', as it was called, continued to be taught in
other Ionian cities.
Excerpt from the Encyclopedia Britannica without permission.