The Museum of the City of New York has an incredible archive of old photos of the city, and they've just uploaded almost 2,000 more documenting the Manhattan Railway Company, who operated the Second, Third, Sixth, and Ninth Avenue elevated train lines. They note, "In 1899 the company began building seven substations and one powerhouse to electrify its steam-powered trains. The photographs span 1900-1905 and document the stages of the modernization project."

During its prime, the system moved a million passengers a day along 102 miles of track and with 334 steam locomotives. For much more on the company, check out Frank K. Hain and the Manhattan Railway Company: The Elevated Railway, 1875-1903, which chronicles the elevated railway, and Hain, who ran it.

Click through for a preview, and you can see the entire collection right here.