Donaldsonville's historic district has what has been described as the finest collection of buildings from the antebellum era to 1933, of any of the Louisiana river towns above New Orleans. Union forces attacked the city, occupying it and several of the river parishes beginning in 1862. Fort Butler was built on the west bank of the Mississippi River. The fort was successfully defended on June 28, 1863, against a Confederate attack. This battle was one of the first occasions when free blacks and fugitive slaves fought as soldiers on behalf of the Union. The fort is listed on the National Register of Historic Places.