Hanzōmon Line

The line was first planned in 1968, alongside the Chiyoda and Yūrakuchō lines, as a relief route for the chronically congested Ginza Line. Its original alignment ran from Futako-Tamagawa on the Tōkyū Den-en-toshi Line to a new station in the Fukagawa district of Kōtō, and during the planning stage it was known simply as Line 11. The designation "Hanzōmon Line" was chosen through a public competition and formally adopted on 1 June 1978, some four and a half years before trains actually reached Hanzōmon Station. Construction had begun in 1972, and the bulk of the line had been expected to open in 1975, but the Teito Rapid Transit Authority (Eidan) lacked the funds to build it on schedule, and the opening slipped.

The first section, the 2.7 km from Shibuya to Aoyama-itchōme, opened on 1 August 1978, immediately offering through-service onto the Tōkyū network via the then-new Shin-Tamagawa Line as far as Nagatsuta. Because providing new Eidan rolling stock would have left more spare cars than cars in service, the line at first ran entirely with Tōkyū 8500 series trains; the first Eidan 8000 series did not enter service until 1 April 1981. The line was extended a short distance to Nagatachō on 21 September 1979, but only as single track, so that during peak hours trains to Aoyama-itchōme and to Nagatachō had to run alternately until the section was doubled.

The next stage proved far more difficult. The original plan would have run the line straight under the Imperial Palace to Ōtemachi, but the route was instead diverted around the north side of the palace, requiring three new stations. The short Nagatachō–Hanzōmon segment (1.0 km) opened on 9 December 1982, ending the single-track operation, but the push onward stalled amid an expropriation battle, as landowners along the route mobilised supporters in opposition. The 4.4 km extension from Hanzōmon to Mitsukoshi-mae finally opened on 26 January 1989 — the first railway extension in Japan of the new Heisei era — well behind its original schedule.

A further 1.3 km extension brought the line to Suitengū-mae on 28 November 1990, and for more than a decade that station stood as its eastern terminus. The last segment, the 6.0 km from Suitengū-mae to Oshiage, opened on 19 March 2003 — the final new section of subway ever opened by the Eidan. It connected the Hanzōmon Line to the Tōbu network and inaugurated reciprocal through-running over the Tōbu Isesaki Line and Tōbu Nikkō Line as far as Minami-Kurihashi, completing a cross-Tokyo trunk linking the south-western suburbs reached by Tōkyū with the north-eastern suburbs served by Tōbu.

On 1 April 2004 the Teito Rapid Transit Authority was corporatised, and the Hanzōmon Line, together with its stations, rolling stock and related assets, passed to the newly formed Tokyo Metro Co., Ltd. The through-services were progressively extended thereafter: from 18 March 2006 Tōbu Isesaki Line trains ran through as far as Kuki, and the line's services now reach Chūō-Rinkan on the Tōkyū side and Kuki and Minami-Kurihashi on the Tōbu side.

Today the Hanzōmon Line is one of the busier subway routes in central Tokyo, carrying just over a million passengers a day, and it remains one of only a small number of Tokyo Metro lines with no above-ground section at all. Its rolling stock has evolved from the early Tōkyū and Eidan trains through the Tokyo Metro 8000 and 08 series to the 18000 series introduced from 7 August 2021, while Tōkyū and Tōbu sets continue to work the line under the three-company through-running arrangement that defines its long, cross-regional services.

• 1968The line is planned, together with the Chiyoda and Yūrakuchō lines, as a relief route for the congested Ginza Line; during planning it is known as Line 11, with an alignment from Futako-Tamagawa to the Fukagawa district.
• 1972Construction begins (the Shibuya–Aoyama-itchōme section is started on 4 June); most of the line had been expected to open in 1975, but a funding shortfall at the Teito Rapid Transit Authority delays it.
• 19781 June: the route, until then Line 11, is formally named the Hanzōmon Line, chosen by public competition; 1 August: the first section, Shibuya–Aoyama-itchōme (2.7 km), opens with through-service onto the Tōkyū Den-en-toshi Line (via the Shin-Tamagawa Line) to Nagatsuta, run initially with Tōkyū 8500 series trains.
• 197921 September: the line is extended to Nagatachō (1.4 km) as single track, so peak-hour trains to Aoyama-itchōme and Nagatachō run alternately until the section is doubled.
• 19811 April: the first Eidan (TRTA) 8000 series trains enter service and Saginuma depot is completed; until then the line had run on Tōkyū stock.
• 19829 December: the Nagatachō–Hanzōmon segment (1.0 km) opens, ending single-track operation on the Aoyama-itchōme–Nagatachō section.
• 19849 April: with the full opening of the Tōkyū Den-en-toshi Line, through-running on the Tōkyū side is extended to Chūō-Rinkan.
• 198926 January: the Hanzōmon–Mitsukoshi-mae extension (4.4 km), routed around the north side of the Imperial Palace, opens after long delays caused by a landowner opposition / expropriation battle — the first railway extension in Japan of the Heisei era.
• 199028 November: a further extension to Suitengū-mae (1.3 km) opens; Suitengū-mae remains the eastern terminus for more than a decade.
• 199520 March: in connection with the Tokyo subway sarin attack, morning operations are suspended and service resumes in the afternoon.
• 200319 March: the final segment, Suitengū-mae–Oshiage (6.0 km), opens — the Eidan's last-ever new subway section — and reciprocal through-running begins over the Tōbu Isesaki and Tōbu Nikkō lines as far as Minami-Kurihashi.
• 20041 April: the Teito Rapid Transit Authority is corporatised; the line and its assets pass to the newly formed Tokyo Metro Co., Ltd.
• 200618 March: through-running on the Tōbu side is extended to Kuki on the Tōbu Isesaki Line; Tōbu introduces 50050 series sets as the 30000 series is withdrawn.
• 20217 August: the Tokyo Metro 18000 series enters service on the line.