Croesus learned of the sudden Persian uprising and defeat of his longtime rivals, the Medes. He attempted to use these set of events to expand his borders upon the eastern frontier of Lydia, by making an alliance with Chaldea, Egypt and several Greek city-states, including Sparta. 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 most favorably, instigating a war that would ironically and eventually end not the Persian Empire but his own.

Croesus began the campaign with an invasion of Cappadocia, crossing the Halys and capturing Pteria, then capital of the district and formidable as a fortress. The city was sacked, and the inhabitants enslaved. Cyrus advanced to halt the Lydian incursion. He incorporated northern Mesopotamia, while receiving the voluntary capitulation of Armenia, Cappadocia, and Cilicia.

Both armies met in the vicinity of the fallen city. The battle appears to have been fierce lasting until nightfall, but indecisive. Both sides sustained considerable casualties; in the aftermath, the outnumbered Croesus withdrew across the Halys. The retreat of Croesus was a strategic decision to suspend operations using winter to his advantage, awaiting the arrival of reinforcements from his allies the Babylonians, the Egyptians and particularly the Spartans. Despite the arrival of winter, Cyrus continued his march on Sardis. The dispersal of Croesus' army exposed Lydia to the unexpected winter campaign of Cyrus, who almost immediately followed Croesus back to Sardis. The rival kings fought again at the Battle of Thymbra, before Sardis, which ended in a decisive victory for Cyrus the Great.