A History of Greek Philosophy / THE SCHOOL OF MILETUS / THALES
The city naturally held a leading place politically as well as commercially. Empire in our sense was alien to the instincts of the Greek race; but Miletus was for centuries recognised as the foremost member of a great commercial and political league, the political character of the league becoming more defined, as first the Lydian and then the Persian monarchy became an aggressive neighbour on its borders.
It was in this active, prosperous, enterprising state, and at the period of its highest activity, that Thales, statesman, practical engineer, mathematician, philosopher, flourished. Without attempting to fix his date too closely, we may take it that he was a leading man in Miletus for the greater part of the first half of the sixth century before Christ. We hear of an eclipse predicted by him, of the course of a river usefully changed, of shrewd and profitable handling of the market, of wise advice in the general councils of the league. He seems to have been at once a student of mathematics and an observer of nature, and withal something having analogy with both, an inquirer or speculator into the origin of things.
To us nowadays this suggests a student of geology, or physiography, or some such branch of physical science; to Thales it probably rather suggested a theoretical inquiry into the simplest thinkable aspect of things as existing. “Under what form known to us,” he would seem to have asked, “may we assume an identity in all known things, so as best to cover or render explicable the things as we know them?”
Cf. Guthrie, The Early Presocratics and the Pythagoreans - A Synopsis of Greek Philosophy
Reference address : https://www.ellopos.net/elpenor/greek-texts/ancient-greece/history-of-philosophy/thales.asp?pg=2