San Nicolás de los Arroyos was founded on 14 April 1748 by Rafael de Aguiar, who gave it its name to honour Saint Nicholas of Bari, now patron of the city.

The closeness to the border between Buenos Aires and two other large provinces made the city a natural stage for the struggle between federalist and Unitarians forces in mid-19th century.
The agreement between thirteen provinces on 31 May 1852, which ratified the Federal Pact and called for a Constitutional Assembly sponsored by Justo José de Urquiza, was signed in this town, and became known as Acuerdo de San Nicolás de los Arroyos.
San Nicolás de los Arroyos was founded on 14 April 1748 by Rafael de Aguiar, who gave it its name to honour Saint Nicholas of Bari, now patron of the city.
The closeness to the border between Buenos Aires and two other large provinces made the city a natural stage for the struggle between federalist and Unitarians forces in mid-19th century. The agreement between thirteen provinces on 31 May 1852, which ratified the Federal Pact and called for a Constitutional Assembly sponsored by Justo José de Urquiza, was signed in this town, and became known as Acuerdo de San Nicolás de los Arroyos.
San Nicolás de los Arroyos