Since ancient times, a combination of skull and crossed bones had been used to mark cemeteries and crypts in Europe. This served as a memento mori, a reminder to all who passed that however fine they felt today, they would someday be just some dusty bones. Pirates found this grim message very helpful in the psychological warfare they waged with ships’ crews. The Jolly Roger, a black flag with skull and crossbones, was adopted as the universal symbol of pirates. The typical pirate tactic was to approach their victims flying a friendly national flag, and then surprise them with a sudden switch to the Jolly Roger, hoping that the crew would panic and surrender or abandon ship without a fight, before any resistance could be organized. According to pirate custom, a crew that offered no resistance would be allowed to flee or be taken prisoner, depending on the circumstances. Prisoners would be ransomed or allowed to join the pirates (a welcome prospect to many ill-fed and mistreated crewmen.) If a crew resisted, the pirates would lower the Jolly Roger and raise a red flag, signifying that no life would be spared.