The Greek Dark Ages were a time of Ionian settlement and consolidation in an alliance called the Ionian League. The Archaic Period of Greece began with a sudden and brilliant flash of art and philosophy on the coast of Anatolia. In the 6th century BC, Miletus was the site of origin of the Greek philosophical (and scientific) tradition, when Thales, followed by Anaximander and Anaximenes (known collectively, to modern scholars, as the Milesian School) began to speculate about the material constitution of the world, and to propose speculative naturalistic (as opposed to traditional, supernatural) explanations for various natural phenomena.