city and port, northern Buenos Aires provincia (province), eastern Argentina, on the western bank of the Paraná River. It was founded in 1748 as San Nicolás de Bari y de los Arroyos by Don Rafael Aguiar and was declared a city in 1819. The Pact of San Nicolás (May 1852), signed there by delegates from the United Provinces of the Río de la Plata, called for a constitutional congress to be held in Santa Fe and named General Justo José de Urquiza (Urquiza, Justo José de) provisional director of the Argentine Confederation.

San Nicolás de los Arroyos is accessible to oceangoing vessels by way of the Paraná River. The city's economy is based on its river trade in grains, iron ore and coal, and manufactured goods. The city's blast furnace produces steel for Argentina's domestic market, and a large thermoelectric station provides power to the city of Buenos Aires and Santa Fe province. Pop. (2001) 125,408.