Cyrus the Great invaded Lydia in order to defeat King Croesus. The Lydians were famed for their proficiency with cavalry. In order to defeat them at their strength, Cyrus mounted his cavalry upon camels instead of horses. For horses naturally fear the smell of camels, unless trained to familiarity. So when Cyrus’s camel troops advanced, Croesus’s horses were unable to stand the smell of them and retreated from the camels, and thusly did Cyrus defeat Croesus.