Japan's First Bridge Across a Strait
The Saikai Bridge (西海橋) is a road bridge across a strait of 1955 in Hario-higashimachi, Sasebo City, to Seihi-cho, Saikai City, Nagasaki Prefecture, and was designated an Important Cultural Property on December 23, 2020 (Agency for Cultural Affairs).
The Agency records a single steel arch with four reinforced concrete rigid-frame spans, 316.2 metres long and 8.2 metres wide, with parapets and end railings; designation number 2720.
An Arch over the Ino-ura Strait
Saikai Bridge carries a road across the Ino-ura Strait (also called the Hario Strait), which joins Omura Bay and Sasebo Bay; designed by the Ministry of Construction, it was completed in 1955 (Agency for Cultural Affairs). Its central steel arch spans 216 metres, the longest in Japan when it was built.
Nagasaki Prefecture says work began on November 23, 1950 and finished on October 18, 1955. Called the Ino-ura Bridge during construction, it was named Saikai Bridge at the opening. Because the current was too fast for supports in the strait, the arch was assembled by hanging its members from cables strung from both shores. Saikai City notes that it opened as a toll road and became free in 1970.
Why It Is an Important Cultural Property
The Agency praises its delicate, structurally rational members, achieved despite post-war shortages, and the outstanding design, fabrication and construction of Japan's first bridge across a strait, the starting point for the country's later long-span bridges. With the Momijidani River garden erosion-control works, it was among the first post-war civil engineering works to be designated an Important Cultural Property, on December 23, 2020.
What to Look For
Nagasaki Prefecture points out that the arch widens towards its feet in three dimensions, both light and stable in appearance. Both shores lie within Saikai Bridge Park, from where the whole arch can be seen (Saikai Bridge Park).
Visiting
Saikai Bridge is still in use as a road bridge. Nagasaki Prefectural Saikai Bridge Park, at Hario-higashimachi in Sasebo, is run by a designated management company (Saikai Bridge Park).
Q&A
- When was Saikai Bridge completed?
- On October 18, 1955 (Nagasaki Prefecture).
- How long is the arch of Saikai Bridge?
- The steel arch spans 216 metres, then the longest in Japan.
- Why is Saikai Bridge an Important Cultural Property?
- It was Japan's first bridge across a strait and the start of its post-war long-span bridges.
- Where can I see Saikai Bridge?
- From Saikai Bridge Park on both shores.
- When was the Saikai Bridge designated an Important Cultural Property?
- On December 23, 2020 (Agency for Cultural Affairs).
Basic Information
| Name | Saikai Bridge (西海橋) |
|---|---|
| Location | Hario-higashimachi, Sasebo City, to Seihi-cho, Saikai City, Nagasaki Prefecture |
| Designation | Important Cultural Property (Structure) |
| Year Designated | Designated 2020/12/23 (Reiwa 2) |
| Quantity | 1 building |
| Dimensions | Steel arch and four reinforced concrete rigid-frame spans, 316.2 m long, 8.2 m wide |
| Owner | Nagasaki Prefecture |
| Public Access | In use as a road bridge (park on both shores) |
References
- Saikai Bridge (Database of National Cultural Properties, Agency for Cultural Affairs)
- https://kunishitei.bunka.go.jp/heritage/detail/102/00005318
- Saikai Bridge (Nagasaki Prefecture cultural properties database, Japanese)
- https://www.pref.nagasaki.jp/bunkadb/index.php/view/783
- National cultural properties (Saikai City, Japanese)
- https://www.city.saikai.nagasaki.jp/soshiki/shakai_kyoiku/kosodate/bunka/bunkazaitou/8118.html
- About Saikai Bridge (Nagasaki Prefectural Saikai Bridge Park, Japanese)
- https://saikaibashi.com/pages/42/
Last verified: 2026.10.15