The Boundary Treaty of 1881 between Chile and Argentina is signed in Buenos Aires.

The Boundary Treaty of 1881 between Argentina and Chile was signed on 23 July 1881 in Buenos Aires by Bernardo de Irigoyen, for Argentina, and Francisco de Borja Echeverría, for Chile, with the aim of establishing a precise border between the two countries based on the uti possidetis juris principle. Despite dividing largely unexplored lands, the treaty laid the groundwork for nearly all of Chile's and Argentina's 5600 km current border.

Buenos Aires, controlled by the government of the Autonomous City of Buenos Aires, is the capital and largest city of Argentina. It is located on the southwest of the Río de la Plata. Buenos Aires is classified as an Alpha− global city, according to the GaWC 2024 ranking. The city proper has a population of 3.1 million and its urban area 16.7 million, making it the twentieth largest metropolitan area in the world.

July 23 is the 204th day of the year in the Gregorian calendar; 161 days remain until the end of the year.