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.

When the motif was revived during the 16th century it was mostly carried by national or political personifications. Its first appearance as an attribute of Liberty in an Italian emblem book was in 1556, later followed by many others. In his "Apotheosis of Venice" (1585) in the Doge's Palace, Paolo Veronese has the ascendant Republic of Venice (personified as a woman) flanked by several symbolic persons, one of whom represents Liberty, dressed as a peasant hoisting a red Phrygian cap on a spear.

The Dutch Maiden, national personification of the Dutch United Provinces fighting to escape from Spanish rule, often carries a hat on a pole. In these cases, the hat is the normal contemporary respectable man's hat, usually with a broad and stiff brim. With considerable cheek, Louis XIV of France had a medal cast in 1678, after the Treaty of Nijmegen ended the war started by his invasion of the Netherlands; this showed the Maiden "standing beside Peace, and receiving the instructions of Prudence".

The imagery was introduced to Britain, partly by the Dutch William III of England, who in one medal presents a cap of liberty to the kneeling England, Scotland and Ireland. When Britannia was pictured as "British Liberty", she usually exchanged the trident she normally carried for a liberty pole. An example of this is a large monument, originally called the "Column of British Liberty", now usually just the "Column to Liberty", begun in the 1750s on his Gibside estate outside Newcastle-on-Tyne by the hugely wealthy Sir George Bowes, reflecting his Whig politics. Set at the top of a steep hillock, the monument itself is taller than Nelson's Column in London, and topped by a bronze female figure, originally gilded, carrying a cap of liberty on a pole.

During the 18th century, the Roman pileus was confused with the Phrygian cap, and this mis-identification then led to the Phrygian cap, familiar from other uses in Roman sculpture, becoming the standard shape when a cap of liberty was used as a political symbol.

The image of Libertas holding a liberty pole can be found on the seals of some British American colonies, notably those of Trustee Georgia and North Carolina.