The history of Rosario differs from that of many other colonial cities in Argentina. It has no exact founding date or official founder, as it emerged and developed organically. The first permanent settlements on the site of the modern city, known then as Pago de los Arroyos (translated as "Land of Streams"), appeared in the 17th century. Initially, it was a sparsely populated rural area with a few farms. In 1724, one of the settlers, Santiago de Montenegro, built a chapel here, where an image of the Virgin of the Rosary was placed, giving the city its future name. In 1751, he was appointed the first mayor.
A key factor in the rise of Rosario was its strategic location on the high bank of the mighty Paraná River. This made it a natural port and trade hub on the route from the country's interior regions to the Atlantic Ocean. Rosario received official city status much later, on 5 August 1852, which gave a powerful impetus to its development. Soon it was declared an international port, and by 1880 it had transformed into Argentina's main export centre, specialising in the shipment of grain and other agricultural produce.
Rapid economic growth in the second half of the 19th century was closely linked to mass immigration. Following the simplification of immigration laws, a stream of settlers from Europe, mainly from Italy and Spain, flocked to Rosario. This led to a rapid population increase: while about 50,000 people lived here in 1887, by 1926 the number had risen to over 400,000, with nearly half of them being immigrants. The city's early economy focused on meat processing, flour milling, and leather industries, as well as the processing of the traditional yerba mate drink. The construction of railways linking the port with agrarian regions further strengthened its status as a "provider city" and a vital transport hub for the country.