Among the Romans the cap of felt was the emblem of liberty. When a slave obtained his freedom he had his head shaved, and wore instead of his hair an undyed pileus. Servos ad pileum vocare is a summons to liberty. In late Republican Rome, the cap of freedmen served as a symbol of freedom from tyranny.
The Liberty Cap as an emblem of liberty was used by the Sons of Liberty as early as 1765. During the American Revolution, particularly in the early years, many of the soldiers who fought for the Patriot cause wore knitted stocking liberty caps of red, sometimes with the motto "Liberty" or "Liberty or Death" knitted into the band.
In addition, there are references of the erection of Liberty Poles, topped with such a cap and flying a Liberty Flag prior to the American Revolution. This was a very popular and powerful symbol in those days.