A liberty pole is a wooden pole, or sometimes spear or lance, surmounted by a "cap of liberty", mostly of the Phrygian cap. The symbol originated in the immediate aftermath of the assassination of the Roman dictator Julius Caesar by a group of Rome's Senators in 44 BCE. Immediately after Caesar was killed the assassins, or Liberatores as they called themselves, went through the streets with their bloody weapons held up, one carrying a pileus (a kind of skullcap that identified a freed slave, not in fact a Phrygian cap) carried on the tip of a spear. This symbolized that the Roman people had been freed from the rule of Caesar, which the assassins claimed had become a tyranny because it overstepped the authority of the Senate and thus betrayed the Republic.

The liberty pole was not thereafter part of the normal Roman depiction of Libertas, the Roman goddess of liberty, who is very often shown holding out a pileus, and carrying a pole or rod. Both refer to the ceremony granting freeman status to a slave, where the subject was touched with the rod, and given the hat. But the hat raised on the end of the pole was shown as an attribute held by Libertas on some coins of the emperor Antoninus Pius, which was enough, with the literary references, to bring it to the attention of Renaissance antiquarians. The pileus itself was shown between two daggers, with the inscription "Ides of March", on some very famous coins made by the assassins of Julius Caesar in the civil war following the assassination.

After the Renaissance, the liberty pole became a common element in the depiction of liberty, initially in a small version carried by personifications, and also later as a larger actual physical object planted in the ground, used as a type of flagstaff.