In late August of 1779, men of the Opelousas Post Militia left from this place to join other militia units to attack British forces in the lower Mississippi Valley. They crossed the Atchafalaya swamp to join Brig. General Bernardo de Gálvez, the Governor of the Spanish province of Louisiana. The O.P.M. met him at Fort San Gabriel a few miles below present-day Baton Rouge. Total forces under Gálvez numbered 175 Spanish army veterans, 330 Spanish recruits, 80 free men of color, 160 Choctaws, plus about 600 men from various militias along the Mississippi River and from throughout the far-flung posts of civilization in Louisiana. On September 22, 1779, Gálvez's effective forces, numbering less than 900, laid siege to and captured Ft. New Richmond at Baton Rouge. This victory forced the surrender of Ft. Panmure at Natchez, British headquarters in the lower Mississippi Valley. This generally unknown military action in American history in which the Opelousas Post Militia took part greatly aided in the winning of the American Revolution of 1775-1783.