An official Confederate port of entry, customhouse and major terminus of the cotton road to Mexico. Cotton was the one great money crop of the South that could be sold to hungry European mills for cash for necessary arms, munitions, drugs that had to come from Europe. International ports on the Rio Grande were the South's frail lifelines, its last resource in a war with an industrialized North that manufactured for its self what the South had to import. Cotton arrived at this booming border town on wagons and oxcarts after a hot and dusty trip. It was then ferried across the river and delivered to the neutral ships anchored in the Gulf.

Teamsters loaded vital leather goods, clothing, blankets, guns, ammunition and medical supplies for the return trip. Troops from nearby Fort Ringgold guarded the wagon trains and town from bandit raids. In November 1863 Federal forces captured Brownsville and the 1st Texas Union Cavalry advanced up river, captured and occupied this town, seizing the cotton awaiting entry. Rio Grande City was reoccupied in May 1864 and used as a supply and reserve base for the recapture of Brownsville. There was constant danger here from raids by Mexican guerrillas paid by enemy agents to make trouble in Texas. Draft evaders, Union sympathizers and those wanting to avoid conflicts of war tried to cross the river here. In an arrangement with Mexican officials, Confederates both required and checked passports to curb desertions and smuggling.