Service on the Yellow Line began on April 30, 1983, adding Archives to the system and linking the two already-built stations of Gallery Place and Pentagon with a bridge across the Potomac River. It was extended beyond National Airport by four stations to Huntington on December 17, 1983, the first station outside the Capital Beltway. When the Green Line link to U Street opened on May 11, 1991, it acted as an extension of the Yellow Line until the southern Green Line branch was completed. When Green Line service began, the Yellow Line was truncated at Mount Vernon Square, where a pocket track exists to relay trains.