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 emergency exits from stations with only a single headhouse. A pair of curved staircases were built from the western ends of the platform; they joined to form a straight staircase above the arch of the tunnel. The exit stairs were completed on September 6, 1904, with a small building in State Street covering them completed on October 10.