In the spring of 1846, the Rio Grande became the center of territorial disputes between the United States and Mexico. Differences started in 1845 when the United States annexed the Republic of Texas and made it the 28th state in the Union. Mexico had never recognized the independence of its former province and insisted that the United States had no right to interfere. Tensions heightened when U.S. President James Polk declared that the Rio Grande formed the boundary of the new state. Mexico drew the boundary of Texas along the Nueces River and saw Polk’s claim as an effort to seize thousands of square miles of additional Mexican land.

When diplomacy failed, Polk ordered U.S. troops to the Rio Grande to establish the river as the boundary. In March of 1846, General Zachary Taylor led an army into disputed land south of the Nueces and raised the Stars and Stripes on the north bank of the Rio Grande across from the Mexican City of Matamoros. Mexico responded with threats and the construction of fortifications across the water. Aware that he was dangerously exposed and that hostilities might arise at any time, Taylor ordered plans for his own fort—a large earthen structure that would become known as Fort Brown.

Construction of the U.S. fort involved considerable thought and effort. Major Joseph King Fenno Mansfield was in charge of designing the fort. After making careful surveys of the surrounding area, he designed a large six sided “star” fort nestled into a bend of the Rio Grande. Each of the walls were to be 10 feet high, 15 feet thick, and extending 125 to 150 yards in length. Large arrow-shaped bastions allowed cannons to be placed at all possible approaches to the fort. A moat, 20 feet wide and 8 feet deep, would surround the entire structure and offer additional protection. The fort was designed to protect about 500 men inside.

The fort was built almost entirely of packed earth. Beginning on April 6, 1846, troops armed with picks and shovels worked around the clock to dig, move, and pack soil into the sturdy protective walls. Trees, fence posts, and barrels were also used to frame protective shelters within the walls. When much of the fort had been completed, on May 1, 1846, General Taylor led most of his troops to a coastal depot to gather supplies to stock the fortification. The final wall of the fort was still under construction on May 3, 1846, when Mexican cannons opened fire on the site.

“We have been here five days. We are about 1800 yards from the center of the city […]. Our flag waved over the waters of the Rio Grande on the 18 March 1846 for the first time. […] It is probably that General Tayor will build a fort for at least one regiment. We have been obliged to reconnoiter and survey for two days in the rain and last night I was up till midnight…”

Captain J.K.F. Mansfield to Colonel Joseph Totten, April 2, 1846. Records of the Office of the Chief of Engineers, Letters Received, National Archives Record Group 77.

Mexican artillerists opened fire on the U.S. fort starting at daybreak on the morning of May 3, 1846 from guns placed in fortifications on the opposite bank of the Rio Grande. These guns showered a heavy rain of metal onto the fort during the first hours of the siege before settling into a sporadic fire that would continue for days.

U.S. troops inside the fort responded to the initial bombardment with a heavy fire of their own. With some carefully directed shoots, they were able to strike one of the Mexican positions and destroy one of the cannons positioned there. Efforts to fire red-hot cannon balls into the city of Matamoros, to set fire to the town, were less successful and quickly abandoned. Because U.S. supplies were limited, fort commander Jacob Brown ordered his gunners to cease firing after several hours to conserve the remaining ammunition. The U.S. troops then endured six days of firing while doing little in response.

Despite the heavy firing, the sturdy fort walls held up well against the barrage. Only two men died during the siege, and several others suffered wounds. The brief period of return fire killed three Mexican soldiers and wounded several others.

The bombardment finally ended on the evening of May 9. As Mexican troops rushed from the battle of Resaca de la Palma, the cannon in Matamoros went silent to avoid striking the retreating men. The shooting never resumed.

”It was very distressing to stand and be fired at all round and not be able to return it in full force and virtue; but, knowing our ammunition was scarce, we reserved it till the death struggle should come on. …Five mortars were playing on us at once, from every point of their works.”

Soldier account of the bombardment of Fort Brown, reported in Niles National Register, June 6, 1846

The original Fort Brown earthworks had a limited life. On May 17, General Zachary Taylor formally named the site Fort Brown, to honor Major Jacob Brown who had commanded the fort during the siege and died in the bombardment. The following day, U.S. troops crossed the Rio Grande and entered Matamoros, making that city their base of operations. No longer vital for defense, the Fort Brown earthworks were abandoned.

The Fort Brown name survived. The war between the United States and Mexico resulted in the establishment of the Rio Grande as the boundary for the two nations, and a new, expanded Fort Brown sprang up several hundred yards away from the original. This post would endure for a century and lend its name to the town that grew around it—Brownsville, Texas.

The post was also significant in other eras. In the 1850s, the troops of the post devoted much effort to halting smuggling and incursions across the Rio Grande. During the Civil War, the fort became a strategic target as Confederates attempted to maintain lucrative cotton trade routes into Mexico and Union forces attempted to halt it. The ongoing Union/Confederate contest for control of the fort also resulted in the last battle of the Civil War at Palmito Ranch on May 13, 1865. In 1916, when violence from the Mexican Revolution threatened to spill across the border, thousands of National Guard troops poured into the area. At the fort, they received valuable training that would be put to use when the United States entered World War I.

The post remained a training ground for soldiers through World War II. As that conflict came to an end, however, Fort Brown was no longer vital to national defense or border protection and the post was decommissioned. Today, buildings of the Fort Brown Reservation remain in use for classrooms and offices of Texas Southmost College.

The original Fort Brown earthworks have suffered from more than 150 years of neglect, carelessness, and destruction. After the fort was abandoned by Zachary Taylor at the end of May 1846, little was done to maintain or preserve the site. By the end of the war with Mexico, almost two years later, the structure had fallen into disrepair and was overgrown with vegetation. During the U.S. Civil War, proposals were made to preserve and improve the old earthworks, but little work was ever done on the site.

Left untended for more than 100 years, the site experienced gradual erosion, then took a direct hit in the 1950s when much of the structure was bulldozed to build a flood protection levee along the Rio Grande. Today, a small section of the ramparts survives near the Fort Brown Memorial Golf Course in Brownsville. That continues to deteriorate as a result of forces of nature, the passage of golf carts and maintenance equipment, and even from the footsteps of well-meaning tourists and history enthusiasts. Traces of the original walls and moat can be detected below ground, but these have also been affected by the construction of irrigation systems, parking areas, and the U.S. Border Wall. The land is now owned by the U.S. International Boundary & Water Commission.

The National Park Service, at Palo Alto Battlefield National Historical Park, is working to document and protect these remains. The park also seeks to provide a variety of on-site programs and displays to preserve the memory of this significant historic site.