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In late Republican Rome, a soft felt cap called the pileus served as a symbol of freemen (i.e. non-slaves), and was symbolically given to slaves upon manumission, thereby granting them not only their personal liberty, but also libertas— freedom as citizens, with the right to vote (if male). Following the assassination of Julius Caesar in 44 BC, Brutus and his co-conspirators instrumentalized this symbolism of the pileus to signify the end of Caesar's dictatorship and a return to the (Roman) republican system.[2][not in citation given]
These Roman associations of the pileus with liberty and republicanism were carried forward to the 18th-century, when the pileus was confused with the Phrygian cap, with the Phrygian cap then becoming a symbol of those values.[3]
https://en.m.wikipedia.org/wiki/Phrygian_cap
In the United States Edit
A Phrygian cap on the Seal of the U.S. Senate.
In the 18th century, the cap was often used in English political prints as an attribute of Liberty. In the years just prior to the American Revolutionary War of independence from Great Britain, Americans copied or emulated some of those prints in an attempt to visually defend their inherited liberties as Englishmen.[8] Later, the symbol of republicanism and anti-monarchial sentiment appeared in the United States as headgear of Columbia,[9] who in turn was visualized as a goddess-like female national personification of the United States and of Liberty herself. The cap reappears in association with Columbia in the early years of the republic, for example, on the obverse of the 1785 Immune Columbia pattern coin, which shows the goddess with a helmet seated on a globe holding in a right hand a furled U.S. flag topped by the liberty cap.[9]
Starting in 1793, U.S. coinage frequently showed Columbia/Liberty wearing the cap. The anti-federalist movement likewise instrumentalized the figure, as in a cartoon from 1796 in which Columbia is overwhelmed by a huge American eagle holding a Liberty Pole under its wings.[9] The cap's last appearance on circulating coinage was the Walking Liberty Half Dollar, which was minted through 1947 (and reused on the current bullion American Silver Eagle).
The U.S. Army has, since 1778, utilized a "War Office Seal" in which the motto "This We'll Defend" is displayed directly over a Phrygian cap on an upturned sword. It also appears on the state flags of West Virginia (as part of its official seal), New Jersey, and New York, as well as the official seal of the United States Senate, the state of Iowa, the state of North Carolina (as well as the arms of its Senate,[10]) and on the reverse side of the Seal of Virginia.
In 1854, when sculptor Thomas Crawford was preparing models for sculpture for the United States Capitol, Secretary of War Jefferson Davis (a slaveowner and later the President of the Confederate States) insisted that a Phrygian cap not be included on a Statue of Freedom, on the grounds that "American liberty is original and not the liberty of the freed slave". The cap was not included in the final bronze version that is now in the building.[11]