Battle of Pteria

At the Battle of Pteria (Πτερία) in 547 BC, the Persian forces of Cyrus the Great fought a drawn battle with the invading Lydian forces of Croesus, forcing Croesus to withdraw back west into his own kingdom.

Background
Formerly, the Lydians and Medes had arranged that the natural boundary between the two empires would be the Halys River. Croesus learned of the sudden Persian uprising and defeat of his longtime rivals, the Medes. He attempted to opportunistically use these set of events to expand his borders upon the eastern frontier of Lydia. He made an alliance with Chaldea, Egypt and Sparta.

Motives
Croesus may have intended re-instating his brother-in-law, Astages on the Median throne. It is also possible that he was trying to pre-empt a Persian invasion of Lydia.

Battle
Cyrus advanced to halt the Lydian invasion. The winter battle appears to have been fierce, but indecisive. Croesus withdrew across the Halys. As Herodotus refers to how the Lydians fell short in defeating the Persians, it seems clear that partly because of the battle, and having fewer troops than the Persians, it was enough for Croesus to retreat. The Persians reclaimed the land of the Medes in their name. In this respect, the battle might be regarded as a strategic victory for the Persians, in that it helped to secure Cappadocia as part of the newly formed Achaemenid Empire.

Aftermath
Among historians, the outcome of the battle remains debatable and unclear. Before all of this, and prior to his invasion, Croesus asked the Oracle of Delphi for advice. The Oracle suggested vaguely that, "if King Croesus crosses the Halys River, a great empire will be destroyed." Croesus received these words with delight, instigating a war that would ironically and eventually end not the Persian Empire but his own. This battle was shortly followed by the Battle of Thymbra, which ended in a decisive victory for Cyrus the Great.