Paso Del Águila (Pass of the Eagle), on the Rio Grande in Maverick County, is a name with an interesting and somewhat complex odyssey. It was originally the name of a ford on the Río Escondido, a short distance below the site of present Piedras Negras, Coahuila, Mexico, near the site of present Villa de Fuente. The road from Presidio del Río Grande to Monclova Viejo, a military outpost on the Río San Rodrigo, crossed the Escondido at that point. Pecan, cypress, oak, and mulberry trees along the banks of the Escondido provided a nesting area for eagles, and flights of eagles to and from this site account for the origin of its name. However, just when it was so named is not known. Although Spanish exploration in this region can be traced back to the seventeenth century, the earliest record of Anglo penetration occurred in the early spring of 1834, when Dr. John Charles Beales and his Dolores colonists crossed the Escondido at this ford and found an American hunter, his wife and children, and a party of five Shawnee Indians trapping beaver. Fifty-six years before the arrival of the Dolores colonists, Fray Juan Agustín Morfi accompanied Teodoro de Croix on his tour of the northern provinces. They left Presidio del Río Grande and headed upriver toward Monclova Viejo by way of the river villages of Santo Domingo, San Nicolás, and La Navaja. On January 29, 1778, they crossed at the Escondido ford and emerged on the plain where Piedras Negras now stands. Morfi noted in his diary that the location was a fine place for a settlement and that water for irrigation could be taken from either the Rio Grande or the Río San Antonio (which empties into the Escondido two leagues from the Rio Grande).
After the Texas Revolution and during the decade of the Republic of Texas, commerce between the towns and villages in northern Coahuila and the Texans was forbidden by Mexican authorities. A clandestine trade did continue, however, between San Antonio and the Mexican settlements, particularly those near the Rio Grande. Replacing the guarded main crossing sites near Presidio del Río Grande was a smuggler's trail that followed a more direct, though northerly, course to San Antonio over which trade caravans moved. The trail left San Fernando de Rosas and crossed the Rio Grande thirty miles upriver from the old presidio at a ford near the mouth of the Río Escondido. Gen. Adrián Woll followed the upper portion of this trail when he raided San Antonio in 1842, and Gen. Isidro Reyes positioned his forces at "El Passo del Águila" when he suspected that the Texans might retaliate by attacking Presidio del Río Grande or San Fernando de Rosas.
In May 1848, just after the Mexican War, Capt. John A. Veatch, an officer in the Texas Mounted Volunteers, maintained an observation post by this smuggler's crossing on the Rio Grande. Although this ford had historically been known as Paso de los Adjuntos del Río Escondido (Pass of the Joining of the Río Escondido), Veatch reported his location as "Eagle Pass," the English equivalent of Paso del Águila. General Reyes's well-known military operations in this area six years earlier had made Paso del Águila an established place name. No longer the name of a ford on the Río Escondido less than two leagues from the Rio Grande, "Paso del Águila" had migrated to the smuggler's crossing by the mouth of the Escondido and supplanted the name Paso de los Adjuntos.
Ten months later Capt. Sidney Burbank, with companies A, B, and F, First Infantry Regiment, arrived at Captain Veatch's campsite on the Rio Grande. Burbank had orders to establish a new post but he bypassed Veatch's location and continued upriver two miles to a more elevated plain, where, on March 27, 1849, his soldiers pitched their tents. He reported his location as "Camp near Eagle Pass, Río Grande, Texas." In November the name of the post was changed to Fort Duncan. Soon after the establishment of the fort, a merchant named Campbell set up a store or trading post at Veatch's campsite across from the mouth of the Río Escondido, and a few Mexicans began to settle in the vicinity. This settlement below the fort was the first American community to be called Eagle Pass.
Almost immediately after the establishment of Fort Duncan, emigrant groups bound for California by way of Mexico began arriving at the Paso del Águila ford. Among the first to cross into Mexico was a party of fifteen men calling themselves the Defiance Gold Hunters' Expedition. They arrived on the Rio Grande on April 21, 1849, less than a month after the establishment of the fort. Other parties of emigrants, varying in size, followed, with names such as the Mississippi Mining and Trading Company, and the Natchez California Company. Some of the forty-niners crossed at Paso del Águila after refitting in the vicinity of Campbell's store. Most, however, camped just north of the fort because of the protection offered by the garrison.
Henry Matson, a member of one of the California parties that broke up there, borrowed a tent from Sergeant Drury, first sergeant of A Company, First Infantry, and with two kegs of liquor opened the first saloon in what became a thriving settlement. Dubbed California Camp, the bustling array of tents and wagons was soon rivaling the older settlement below the fort. John Twohig, a San Antonio banker, who owned much of the land along the river, laid out a plan for the town in 1850 and gave it the name Eagle Pass. Writer Cora Montgomery (pseudonym for Jane Cazneau) and her husband were among the first settlers in 1850, and she described Eagle Pass as a "two-headed child, with one face looking above and the other below Fort Duncan." Caravans of freight wagons, which had once gone to Presidio del Río Grande, and more recently to the smuggler's ford below Fort Duncan, began arriving at the growing settlement above the fort. That same year, 1850, a military garrison was established on the opposite bank of the Rio Grande from Fort Duncan, and the village of Piedras Negras was founded with the arrival of settlers from the nearby river towns. With the settlement of Eagle Pass firmly established above the fort, the older Eagle Pass, two miles downriver, rapidly waned and eventually disappeared.