Herodotus and the Dating of the Battle of Thermopylae

The battle of Salamis can be dated with a high degree of certainty. Probably about the time of that battle, Cleombrotus was at the Isthmus, constructing the defences there. At some point while building the wall, he considered giving chase to the Persian army. When his sacrifice was answered by a solar eclipse, he took this as a bad omen and immediately returned to Lacedaemon. The eclipse visible to Cleombrotus could only have been that of 2 October 480. Now it is generally supposed that Cleombrotus would not have thought to abandon the construction of the wall and pursue Xerxes unless the latter had just begun his retreat from Athens. Thus, as Herodotus says that a few days () after the battle of Salamis Xerxes withdrew from Attica, the battle of Salamis probably occurred before 2 October 480.