1904 - October 27 – The first underground line of the New York City Subway opens.

On October 27, 1904, the first underground line of the New York City Subway system opened, marking a significant milestone in the city's transportation history. The line, known as the Interborough Rapid Transit (IRT), ran from City Hall in lower Manhattan to 145th Street and Broadway in Harlem, covering a distance of about 9 miles. The subway line was a response to the city's rapidly growing population and increasing congestion on the streets above.

The opening of the subway line was a major event, drawing huge crowds eager to experience this new mode of transportation. The subway cars were hailed as modern marvels, featuring electric lights, comfortable seating, and efficient travel times.