Meitetsu Seto Line

The line owes its existence to the pottery town of Seto, long a centre of ceramics (Seto ware) with a strong demand for freight haulage. After local efforts failed to draw the state-built Chūō Main Line directly to Seto, the government agreed instead to open a connecting station at Ōzone, and Seto businessmen led by Katō Mokuzaemon raised the capital to build a line out from Seto. The company, Seto Automatic Railway (瀬戸自動鉄道), opened the first section between Yada and Seto (today's Owari Seto) on 2 April 1905 — the second-earliest opening among today's Meitetsu lines — and extended it to Ōzone in 1906. Passenger service was at first worked by Serpollet-type steam railcars, Japan's first use of self-propelled rail motor cars; underpowered and prone to stalling on grades, they prompted the firm to rename itself Seto Electric Railway (瀬戸電気鉄道) in December 1906 and to electrify the Ōzone–Seto section at 600 V DC in 1907.

Even after electrification the Chūō Main Line's Ōzone station was slow to open, so the company pressed on toward central Nagoya in parallel. To transship Seto's ceramic ware and other freight onto cargo boats on the Horikawa canal, it built the so-called "Outer Moat Line" along the moat of Nagoya Castle. The Ōzone–Doigeshita section opened on 23 May 1911 and the line reached Misono (later Horikawa) that September; the moat alignment, threaded along the bottom of the castle's outer moat, required unusual engineering, including a gauntlet single-track section and a sharp 60-metre-radius curve. The whole line was completed on 18 January 1915 when the final six-chain (about 120-metre) segment opened and Horikawa Station came into use. With the Chūō Main Line's Ōzone station having opened in 1911, the Seto Line now linked the national railway at Ōzone and the canal at Horikawa, becoming a major artery for the freight of Nagoya and Seto.

During the inter-war years the line was converted from a tramway under the Tramways Act to a railway under the Local Railway Act in 1921, when Seto Station was renamed Owari Seto, and it was progressively double-tracked, all but a few gauntlet sections being doubled by December 1929. Freight long made up a large share of revenue, but competition from buses and the slump in Seto's ceramic industry during the Shōwa Depression eroded the company's finances. Amid wartime consolidation of transport under government direction, and coinciding with the 1935 creation of the present Nagoya Railroad through the merger of Nagoya and Aichi Electric railways, Seto Electric Railway merged into Meitetsu on 1 September 1939, becoming its Seto Line.

In the post-war years the line was rebuilt and modernised, spurred in part by the line's worst accident, a derailment and overturning between Inba and Ōmori on 5 January 1948 that killed and injured many New Year shrine-goers. Meitetsu regarded the Seto Line as an important suburban route, but its connection into the heart of Nagoya — the legacy moat route to Horikawa, with its gauntlet at Honmachi and tight curves — was a bottleneck, and the company's long-term aim was to replace it with a wholly new line into the city centre. Successive plans from 1950 onward to through-run the line into the city's planned subway network foundered over gauge, third-rail and cost questions, and in 1962 the Nagoya mayor formally told Meitetsu that sharing track with the subway was undesirable.

After through-running with the municipal subway was abandoned, Meitetsu resolved to build its own underground line into the city. As part of a wider agreement, Meitetsu ceded to the city the Yagoto–Akaike licence that overlapped the planned Subway Tsurumai Line, in return for the city's consent to its new Seto Line tunnel to Sakae and for the new Toyota Line and through-running with the Inuyama Line. The relevant licences were approved on 18 May 1972, and a groundbreaking ceremony for the Sakaemachi extension was held on 30 January 1976. With construction under way, the obstructing "moat" section was abolished: the Horikawa–Higashiōte stretch was withdrawn on 15 February 1976 (the Higashiōte–Doigeshita portion suspended), and Horikawa–Doigeshita was replaced by buses. Freight services ended on 15 February 1978, the line was raised to 1,500 V DC on 19 March 1978, and on 20 August 1978 the underground extension to Sakaemachi opened, realising Meitetsu's long-cherished goal of reaching the city centre; the new terminus took the name Sakaemachi, the name the subway's Sakae station had used until 1966.

The Sakaemachi extension transformed the Seto Line into one of Meitetsu's busiest routes, and the company spent the following decades coping with surging ridership and modernising the line. Stretches in the city were elevated — Morishita–Yada in 1983 and Higashiōte–Morishita by 1990 — and rolling stock was renewed, air-conditioning reaching 100 percent in 1990. The line carried IC ticketing from 2011 with the introduction of manaca, the last of the older cars gave way to the modern 4000 series in 2014, and the 3300 series entered service in 2016. A grade-separation project around Kitayama Station continued into the 2020s, with the up track elevated on 19 March 2022 and the down track on 26 July 2025, completion of the wider scheme being targeted for fiscal 2026.

• 19052 April: Seto Automatic Railway opens the first section, between Yada and Seto (today's Owari Seto), worked by Serpollet-type steam railcars.
• 19061 March: the line is extended from Yada to Ōzone. On 18 December the company renames itself Seto Electric Railway.
• 190717 March: the Ōzone–Seto section is electrified at 600 V DC and electric-car operation begins.
• 191123 May: the Ōzone–Doigeshita section of the 'Outer Moat Line' opens; in September the line reaches Misono (later Horikawa). The Chūō Main Line's Ōzone station also opens this year.
• 191518 January: the final six-chain (about 120 m) segment opens, completing the line, and Horikawa Station comes into use.
• 192113 April: the line is converted from a tramway under the Tramways Act to a railway under the Local Railway Act. On 19 February Seto Station had been renamed Owari Seto.
• 1929December: double-tracking is largely completed, leaving only a few gauntlet sections beyond Doigeshita on the 'moat' stretch single-tracked.
• 19391 September: Nagoya Railroad (Meitetsu) merges Seto Electric Railway; the route becomes the Seto Line.
• 19485 January: a train carrying New Year shrine-goers derails and overturns between Inba and Ōmori, the worst accident in the line's history.
• 197218 May: the licences for the new Sakae underground line are approved after Meitetsu cedes the overlapping Yagoto–Akaike licence to the city.
• 197630 January: groundbreaking for the Sakaemachi extension. On 15 February the Horikawa–Higashiōte 'moat' section is withdrawn and bus substitution begins on Horikawa–Doigeshita.
• 197815 February: freight services end. 19 March: the line is raised from 600 V to 1,500 V DC. 20 August: the underground extension to Sakaemachi opens, finally reaching central Nagoya.
• 1983Morishita–Yada is elevated as part of a wider grade-separation of the line within Nagoya.
• 199030 September: the down track of Higashiōte–Morishita is elevated, completing that section's grade separation; air-conditioning of the fleet reaches 100 percent.
• 20146 April: the last 6000-series cars run their farewell service, leaving the 4000 series as the line's sole rolling stock.
• 202526 July: the down track around Kitayama Station is elevated, the down-track stage of a grade-separation project whose full completion is targeted for fiscal 2026.