Alonso de Vera y Aragon set out from Asuncion in mid-March 1585 with 135 soldiers, a thousand horses, fifty yokes of oxen, and more than 300 cattle -- one of the largest expeditions ever to leave Asuncion for a founding. Many of his recruits were mestizo, and some were drawn by the legend of the Laguna de las Perlas, a lake supposedly rich with pearl-producing oysters near the Bermejo River. The legend proved false, but on April 14, 1585, Vera founded La Concepcion de Nuestra Senora anyway. The city's economy depended entirely on the encomienda system, which subjected indigenous people to forced labor. Concepcion's population reached perhaps 500 Spaniards, but the encomienda communities of Matara and Guacara -- where hundreds of indigenous people were compelled to produce linen, cotton, wax, and hemp -- were the real engine. Without that coerced labor, the city had nothing.

The indigenous nations of the Chaco were nomadic, warlike, and culturally diverse in ways that made them nearly impossible to govern by Spanish methods. Evangelization failed with most groups. Agricultural labor under the encomienda system was alien to their way of life. Resentment built year by year. In 1595, a forced recruitment of indigenous people for transfer to Asuncion provoked a general uprising. Raids on the city intensified -- in 1599 alone, two major assaults nearly overran Concepcion. Aid came sporadically from Asuncion, Corrientes, and Santa Fe, but the distance and difficulty of the terrain made sustained defense impossible. When a jurisdictional change in 1617 transferred Concepcion from Asuncion's authority to the distant Governorate of Buenos Aires, the lifeline was effectively severed. Buenos Aires saw no profit in maintaining a remote outpost outside its trade routes to Lima.

In 1631, a coalition of indigenous groups launched a devastating attack on Matara, the principal encomienda settlement linked to Concepcion. Much of the city's garrison died in the defense. The survivors, understanding their position was no longer tenable, undertook a painful march on foot to Corrientes. Archaeological evidence shows that Concepcion was burned immediately after its abandonment and reoccupied by an indigenous community. A captain writing from Corrientes reported that the refugees should give infinite thanks to God for being alive. A priest who witnessed their arrival described it as painful to see those men, yesterday so prosperous and today miserable begging for alms. Multiple expeditions attempted to reoccupy the site between 1634 and 1640, but each failed. In 1645, a Royal Cedula dissolved Concepcion's Cabildo, and its inhabitants were officially absorbed into Corrientes.

The ruins remained hidden for three centuries, partly because historians assumed the city must have stood on the banks of the Bermejo River -- the name "del Bermejo" seemed to demand it. In reality, Concepcion lay roughly 60 kilometers west of the river. When Alfredo Martinet stumbled upon pottery fragments in 1943 along the former National Route 95, most experts refused to believe the site could be Concepcion. It took until 1958 for the newly created Faculty of Humanities at the National University of the Northeast to begin systematic excavation, and until 1970 for historian Eldo Morresi to definitively confirm the identification. The site -- declared a National Historic Place -- covers approximately 30 hectares, with five streets running each direction, all 12 meters wide. Facing the main plaza's north side stands the Catholic temple, exactly where the Laws of the Indies dictated it should be in an inland city. Over 600 archaeological pieces were found during a 2007 excavation alone.