The Subte was born of a city racing to remake itself. By 1900 Buenos Aires had one of the most extensive tramway networks in the world, and it was choking on its own success, the lines monopolized and overwhelmed. The underground was part of a broader transformation: water and sewage systems completed in 1886 and steadily expanded, streets paved, a colonial town reinventing itself as a modern capital. There was even a practical political motive. When officials decided in 1894 to build the Congress in its present location, the subway promised to shorten the trip between the legislature and the Casa Rosada, linking the two poles of Argentine power beneath the ground. The Anglo-Argentine Tramways Company, granted permission in 1909, built that first stretch of Line A between Plaza de Mayo and Plaza Miserere.

The trains that opened Line A would still be running when their grandchildren rode them. Built by the Belgian firm La Brugeoise et Nivelles between 1911 and 1919, the wooden cars rattled through the tunnels of Line A from 1913 until January 2013, a full century of service. By the end they had become the oldest underground rolling stock in commercial use anywhere in the world, varnished wood and brass fittings carrying commuters who pulled out smartphones to photograph the antique they were riding to work. When they were finally retired in favor of new Chinese-built cars, Argentina passed a law in December 2013 protecting the entire fleet, ensuring the survivors would go to museums and restorers rather than scrapyards. Some now sit in parks; others wait in the Polvorin workshop for a second life.

Today six lines, labeled A through E and H, thread 56.7 kilometers of track through 90 stations, joined by a surface premetro feeder that opened in 1987. The network grew up under three separate private companies in its early decades, an arrangement that left lasting scars: Line B was built to a different electrification system and different measurements than its siblings, a quiet incompatibility that still complicates the rolling stock a century later. The state nationalized the whole system in 1939, then handed it back to private operators in the 1990s. By 1995 the firm Metrovias ran the Subte; in December 2021 the operator Emova took over the concession. Through every change of hands, one thing stayed constant: the tunnels, tracks, and trains remain the property of the city itself.

More than a million passengers descend into the Subte every day, and the system feels every one of them. Built fast in the early twentieth century and expanded only fitfully since, the network is chronically overcrowded, its routes spreading from the Plaza de Mayo like branches of a tree. Ambitious plans pile up faster than tunnels get dug. Law 670 envisions three new lines; a rival plan called PETERS imagines a different future entirely. Yet for the first time in half a century, since 2019 not a single new line has been under construction. The Subte endures instead as a working monument, the cost of a ride climbing with each devaluation of the peso, the historic Line A still tracing the route it cut beneath the Avenida de Mayo when the twentieth century was new.