Procession of the Black Breeches
This is the heading of a chapter in vol. ii. of Carlyle's French Revolution. The chapter contains a description of the mob procession, headed by Santerre carrying a pair of black satin breeches on a pole. The mob forced its way into the Tuileries on June 20th, 1792, and presented the king (Louis XVI.) with the bonnet rouge and a tricolour cockade.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894