The Eclipse of Thales and the Battle of Halys

Today everyone was excited about the total solar eclipse (near-total in some places) that occurred this afternoon over the continental United States. We all knew that the eclipse was going to happen decades in advance due to modern astronomical calculations, but, in ancient times, there was no sound way of predicting when an eclipse would occur… until Thales of Miletos came along.

According to the Greek historian Herodotos of Halikarnassos, the early astronomer and mathematician Thales of Miletos accurately predicted the date of a solar eclipse.[1] Unfortunately, Herodotos never explains how Thales did it, which leaves modern historians to guess at what ingenious calculations this ancient Einstein might have employed. The eclipse is now though to have been one which occurred on May 28, 585 B.C.[2]

Other historians, meanwhile, maintain that Herodotos’s report is nothing but a legend and that it would have been impossible for Thales to have accurately predicted the date of a solar eclipse, since the astronomical knowledge available at the time would have been totally insufficient.[2]

Herodotos also reports that, on the same day when the eclipse occurred, the Lydians and the Medes were marching into battle against each other. The two nations had been at war for many years. Then, in the midst of the battle, the moon passed in front of the sun, blocking out the light and causing day to turn to night. Both sides interpreted the eclipse as an omen from the gods; they ceased fighting and decided to reach a truce instead.[1] The location of the battle, which Herodotos does not specify, is believed by modern historians to have been the Halys River in Asia Minor.[2]

[1] Herodotos, The Histories 1.74.2
[2] Leloux, Kevin. “The Battle of the Eclipse (May 28, 585 BC): A Discussion of the Lydo-Median Treaty and the Halys Border.” Polemos. Volume 19, no. 2, 2016, ISSN 1331-5595, pp. 31–54, particularly 37–39, 49.
[3] Mosshammer, Alden A. “Thales’ Eclipse.” Transactions of the American Philological Association. Vol. 111, 1981, pp. 145–155.

Author: Spencer McDaniel

I am a historian mainly interested in ancient Greek cultural and social history. Some of my main historical interests include ancient religion and myth; gender and sexuality; ethnicity; and interactions between Greeks and foreign cultures. I hold a BA in history and classical studies (Ancient Greek and Latin languages and literature), with departmental honors in history, from Indiana University Bloomington (May 2022) and an MA in Ancient Greek and Roman Studies from Brandeis University (May 2024).

2 thoughts on “The Eclipse of Thales and the Battle of Halys”

    1. There is no “proof” of the story. Herodotos wrote about it in his Histories and all we have for it is Herodotos’s word. As I mentioned in the article, many historians believe that the story of Thales predicting the eclipse is probably apocryphal.

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