San Nicolás de los Arroyos is a city located in the province of Buenos Aires, Argentina. Situated on the western shore of the Paraná River, it lies approximately 61 kilometers (38 miles) from the city of Rosario. The city serves as the administrative seat of the partido of San Nicolás de los Arroyos and has a population of about 133,000 inhabitants.
The city is sometimes referred to as Ciudad de María because of a series of Marian apparitions that occurred there. These events led to the construction of the Sanctuary in honor of Our Lady of the Rosary of San Nicolás, which began in the 1980s. In 2016, Bishop Cardelli of the diocese officially approved these apparitions as "worthy of belief."