A male peacock displays his feathers to show his fitness. Utilizing the Handicap Hypothesis imo. A human equivalent might be growing a long beard. Something that would be a liability in a fight because your enemy could grab it and use it to their advantage.
Scenario: A plague wipes out the Kushan, Parthian, Hatra, and Osroene nations sometime around 200 AD. The Romans and Hans send in their full military force to conquer the undefended lands. Eventually the two armies meet and a war erupts.
Scenario 2: Roman Army start in Fort Collins CO, Han Army start in Pueblo CO. State in un-populated.