The eagle's challenge achievements are skill based milestones in the game Assassin's Creed. Players can obtain the eagle's challenge achievement by slaying 25 soldiers in a single fight. The easiest way to obtain this achievement is near the entrance of Jerusalem. Players should attack a guard. This will make the guards chase after Altair. Let the guards follow and then run past larger groups of guards until there are 25 total.GameFAQs: Assassin's Creed Achievement Guide