A solar eclipse occurs, as predicted by the Greek philosopher and scientist Thales, while Alyattes is battling Cyaxares in the Battle of the Eclipse, leading to a truce. This is one of the cardinal dates from which other dates can be calculated. It is also the earliest event of which the precise date is known.

The eclipse of Thales was a solar eclipse, which was, according to the ancient Greek historian Herodotus, accurately predicted by the Greek philosopher Thales of Miletus. If Herodotus' account is accurate, this eclipse is the earliest recorded as being known in advance of its occurrence. According to Herodotus, the change of day into night was interpreted as an omen, and interrupted a battle in a long-standing war between the Medes and the Lydians in Anatolia. The only solar eclipse matching the presumed place, era, and conditions of visibility necessary to explain the historical event is the eclipse of 28 May 585 BC. How exactly Thales could have predicted a solar eclipse remains uncertain, however, and modern scholars are skeptical of the story's veracity. Some have argued for different dates, or for other interpretations of Herodotus's account.