Midōsuji Line
The network's first service, the Midōsuji Line from to , opened in 1933. As a north–south trunk route, it is the oldest and busiest line in the whole network. Both it and the main east–west route, the Chūō Line, were later extended to the north and east, respectively. These extensions are owned by other railway companies, but both Osaka Metro and these private operators run their own set of trains through between the two sections.