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Additional tunnels soon followed, including a route beneath Cornhill Street serving stations like Skully Square and Adam Square, linked to the now-defunct tunnels under City Hall Plaza. The system extended into neighborhoods like Roxbury via lines from South End, with certain platforms and portals—such as the one at Boilston Street—still visible today behind fences.
The System’s Prime and Gradual Decline
By the turn of the 20th century, Boston had established an intricate subterranean rail network, an underground city beneath the surface, designed to alleviate congestion. Yet, despite its early success, signs of decline emerged almost as soon as the system was operative.