A floppy hat of ancient design, somewhat resembling a benippled nightcap, or the psilocybian mushrooms which bear its name. Often made from red felt. Worn by Marianne, the figure of Liberty in La Liberte Guidant le Peuple, the famous painting by Delacroix which depicts the French revolutionary struggle. Often shown sitting atop a flagpole or pike, which is then called a 'liberty pole'.

In Roman times, when a slave was freed, the ritual included the presentation of a pileus libertatis ("liberty cap") to the newly-freed slave, who benefited because the ex-slave's close-cropped hair, unfashionable and stigmatising, a mark of servitude or criminality, was covered while it grew.

It's sometimes known as the 'Phrygian Cap', after Phrygia, a kingdom which dominated western and central Asia Minor around 800 BC. The Persian god Mithras, who is commonly depicted wearing one, was very popular with Roman legionaries. Many Roman slaves came from Phrygia.

It was worn extensively by Scythians, including the Athenian police force, the Scythotoxotes or Scythian Archers, mercenaries who were a sort of Hell's Angels of the day - scary barbarians on souped-up mounts with custom paint jobs. After the Romans conquered Greece the Scythian police were kept on and perhaps this is one route taken by the Cap on its way into classical Europe.

Saturninus, when he took the Roman Capitol in 263, stuck a Liberty Cap on the end of his spear, and hoisted it up so that it could better be seen, symbolising the emancipation he promised to all slaves who joined his forces. Others (including Marius and the murderers of Julius Caesar) were said to have followed his example in exhibiting spear-hoisted Liberty Caps to symbolise liberation for the masses at tricky points in their careers.

The Cap appears in several iconographies dating from the 16th Century, such as the 'Iconologia' of Cesare Ripa (1593), which emphasised the connections with the manumission (slave-freeing) ceremony.

As Europe lurched into the Enlightenment, the Liberty Cap, as it was to become known, was widely adopted as a symbol of freedom from political tyranny by the various groups, some of them masonic, who were plotting revolutions (and later carried them out.) One early example, in Brittany in 1675, was the "Revolt of Red Caps" - a series of riots protesting unfair tax laws.

As some of these conspirators rose to political power, notably in France, the Cap (known as the bonnet rouge, or bonnet de la liberte) became prominent in many expressions of the newly conceived hope for liberty, as for example in Augustin Dupre's depiction of Liberty as a young woman in the Libertas Americana Medal of 1783, which shows a pole supporting a Liberty Cap (a 'liberty pole') behind her head.

It was part of the uniform of the Sans-Culottes. Louis XVI was forced to wear the Cap and drink the health of the people when the Tuileries were taken. After the revolution, the Cap was everywhere, from milestones to official documents. Donning a Liberty Cap became de rigueur for all members of the Assemblies.

There were close links between the French Revolution and the American struggle for Independence. In 1765 the Cap was used by the Sons of Liberty and many Patriot soldiers in the American Revolution wore Liberty Caps bearing the phrase "Liberty or Death". After the revolution, many coins, for example the 1793 Liberty Cap Half Cent (inspired by Dupre's medal, above), and other paraphernalia of state, such as the seals of the US Army and Senate, showed Caps, often on poles.

In the 1820's, the Liberty Cap meme spread to the South Americas, where fresh revolutions were hatching. It now appears, for example, on the flags or other insignia of the Argentine army and navy, Haiti, El Salvador, Paraguay and the Brazilian state of Santa Catarina.

Back in the US, the original design for a statue of 'Lady Freedom', produced in 1855 by the sculptor Thomas Crawford, was for an "Armed Liberty" wearing a Liberty Cap.

Ironically, the associations with freed slaves proved too much for Jefferson Davis (then the War Secretary and later the president of the Confederacy), who objected to the design. When the statue was erected atop the Capitol dome in 1863 the Liberty Cap had been swapped for a helmet with an Iroquois eagle headdress.