under Boston Harbor. Construction started near the eastern terminus in Maverick Square, as the route in downtown Boston was not yet determined. Not until July 25, 1901 did the Commission determine that the Tunnel would run under State Street, with a station at Atlantic Avenue next to busy Long Wharf. The station was constructed in two sections under separate contracts. "Atlantic Chambers", which served as the west end of the underwater portion of the tunnel, was built in an open cut just west of Atlantic Avenue; it housed the elevators and stairways to access the station as well as the ticket booths. The main arched station, to the west of Atlantic Chambers, was built with drifts. The two side platforms were long, wide, and below the surface. Atlantic Chambers was a rectangular shaft measuring by , divided by three floors into four smaller chambers. The reinforced concrete walls were between thick. At the east end of each platform was a space for elevators and stairs; these two rooms and the trackway between them occupied the lowest chamber. Construction of Atlantic Chambers began on December 5, 1901, and excavation was complete by May 29, 1903. On June 19, 1903, compressed air in the tunnel to the east blew out the bulkhead into Atlantic Chambers, killing two workers. This air pressure had been necessary to keep water from seeping into the tunnel; after the accident, Atlantic Avenue settled slightly above the tunnel. It was necessary to use additional dunnage to limit sagging of the elevated line above; even so, elevated operations were impacted from June 20 to October 7, 1903. Unlike other early stations in Boston, which were built with cut-and-cover tunneling, most of Atlantic Avenue station was built as a large barrel vault. Drifts were first used to construct the vertical station walls, then the crown of the arch. Transverse sections of the arch were then completed, followed by the invert. The arch was wide and tall; the walls of the station were thick and the arch thick. Work began on this section on March 17, 1902; the last section of arch was completed on June 26, 1903. The rough work of the station vault was completed on August 28, 1903, with the tilework finished on January 19, 1904, and the granolithic platforms on February 10. The Paris Métro train fire in August 1903 led the BTC and BERy to desire