The Toei Asakusa Line was the first subway line constructed by the Tokyo Metropolitan Government. The line number is Line 1, because it was technically the first subway line in Tokyo to be planned in the 1920s as an underground route connecting the Keikyu and Keisei Electric Railway via , eventually allowing for through trains between these two railways. In its original plan form, the line would have actually bypassed Asakusa Station entirely. However, the plan was changed to take advantage of the existing Tobu Isesaki Line (section now named as the Tobu Skytree Line) and Tokyo Metro Ginza Line connections at Asakusa.