Inland Sea

From Academic Kids

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The Inland Sea and its major straits with the bay of Osaka (dashed)
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The torii of Itsukushima Shrine is one of the most popular tourist spots of the Inland Sea.

Formally named the Seto Inland Sea (瀬戸内海 Seto Naikai), the Inland Sea is the body of water separating Honshu, Shikoku, and Kyushu, three of the main islands of Japan. It serves as an international waterway, connecting the Pacific Ocean to Sea of Japan. It connects to Osaka Bay and provides a sea transport link to industrial centers in the Kansai region, including Osaka and Kobe. Before the construction of the Sanyo Main Railroad Line, it was the main transportation link between Kansai and Kyushu.

Yamaguchi, Hiroshima, Okayama, Hyogo, Kagawa, Ehime, Fukuoka and Oita prefectures all have coastline on the Inland Sea; the cities of Hiroshima, Iwakuni, and Matsuyama are also located on it.

The Inland Sea region is known for its moderate climate, with a stable year-round temperature and relatively low rainfall levels: the area is often called "the land of fair weather" (晴れの国 hare no kuni). The sea is also famous for its periodic red tides (赤潮 akashio) caused by dense occurrences of certain phytoplankton and resulting in the death of large numbers of fish.

Since the 1980s, its northern and southern shores have been connected by the three routes of the Honshu-Shikoku Bridge Project, including the Great Seto Bridge, which serves both railroad and automobile traffic.


Geographical features

The Inland Sea is 450 km long from east to west. The width from south to north varies from 15 to 55 km. In most places, the water is relatively shallow. The average depth is 37.3 m; the greatest depth is 105 m.

The Naruto Strait connects the eastern part of the Inland Sea to the Kii Channel, which in turn connects to the Pacific. The eastern part of the Inland Sea connects to the Sea of Japan through the Kanmon Straits and to the Pacific through the Bungo Channel.

Each part of the Inland Sea has a separate name in Japanese. There are also many straits which are located between the major islands, as well as a number of smaller ones that pass between islands or connect the Inland Sea to other seas or the Pacific.

Almost 3,000 islands are located in the Inland Sea, including the larger islands Awajishima and Shōdoshima. Many of the smaller islands are uninhabited.

Major islands on Inland Sea


Over 500 marine species are known to live in the Inland Sea. Examples are the ayu, an amphidromous fish, the horseshoe crab, the finless porpoise and the great white shark, which has occasionally attacked people in the Inland Sea.


It is believed that in the last ice age the sea level was lower than today. After the ice age, sea water poured into a lower part between the Chugoku mountains and Shikoku mountains and formed the Island Sea as we know it today.

From ancient times, the Inland Sea served a main transport line between its coastal areas, including what is today the Kansai region and Kyushu. It was also a main transport line between Japan and other countries, including Korea and China. Even after the creation of major highways such as the Nankaido and San'yodo, the Inland Sea remained a major transport route. There are records that some foreign emissaries from China and Korea sailed on the Inland Sea.

Due to the importance of water traffic, regional powers often had their own private navies. In many documents, these navies are called suigun (水軍, water army), or simply pirates. Sometimes they were considered to be public enemies, but in most cases they were granted the right to self-governance as a result of their strength.

In the 12th century, Taira no Kiyomori planned to move the capital from Kyoto to a coastal village Fukuhara (today Kobe) to promote trade between Japan and the Song Dynasty of China. This transfer was unsuccessful, and soon after Kyoto became the capital again.

During the feudal period, suigun seized power in most coastal areas. The Kono in Iyo province (today Ehime prefecture) and Kobayakawa (later Mori) in Aki province (today a part of Hiroshima prefecture) clans were two of the more famous suigun lords.

In the Edo period, the Inland Sea was one of the busiest transport lines in Japan. It was a part of a navigational route around Japan's islands via the Sea of Japan. Many ships navigated from its coastal areas to the area along the Sea of Japan. It was not only the main transport line between Kansai and Kyushu, but also for Hokuriku, Tohoku, and even Hokkaido (which was called Ezo at the time). Major ports in the Edo period were Osaka, Sakai, Shimotsui, Ushimado, and Tomonoura. The Inland Sea also served many daimyo in the Western area of Japan as their route to and from Edo, to fulfill their obligations under sankin kotai. Many used ships from Osaka. Thanks to transport through the Inland Sea, Osaka became the economic center of Japan. Each han had an office called Ozakayashiki in Osaka. These Ozakayashiki were among Japan's earliest forms of banks, facilitating domestic trade and helping to organize the income of the daimyo, which was in the form of koku, giant bales of rice.

The Inland Sea was also part of the official Chosendentsushi route, bringing Korean emissaries to the Shogunate.

After the Meiji Restoration, the coastal areas of the Inland Sea were rapidly industrialized. One of the headquarters of the Japanese Navy was built in the town of Kure. Since the Meiji period, development of land transport has been reducing the importance of the Inland Sea as a transport line. Remarkable land transportation innovations include the Sanyo Main Railroad Line in Honshu, Yosan Main Railroad Line in Shikoku, completed before World War II, and three series of bridges connecting Honshu and Shikoku, which were completed in the late 20th Century. The Inland Sea still serves, however, both an international cargo transport line and several local transport lines connecting Honshu with Shikoku and Kyushu.


The coastal area of the Inland Sea is one of most industrialized areas in modern Japan. Besides Osaka, Kobe and Hiroshima, some other major industrial cities are Kurashiki, Kure, Fukuyama, and Ube in Honshu, and Sakaide and Niihama in Shikoku. Innoshima is also known for its ship factory.

The main industries are steel production, ship construction and since 1960s oil refining and oil derived production.

Thanks to the moderate climate and beautiful landscape, fishing, agriculture and tourism bring a lot of income to the area as well.


Today the Inland Sea serves its coastal areas mainly for two purpose: first international or domestic cargo transportation and second local transportation between coastal areas and islands on it. Major ports are Kobe, Okayama, Takamatsu, Tokushima, Matsuyama and Hiroshima. Honshu and Shikoku are connected with three series of bridges since the late of 1980s, constructed since 1970s. Those series of bridges are from east to west, Akashi-Kaikyo Bridge, Great Seto Bridge, Setouchi Shimanami Kaido Express. On the other hand, no bridge over the Inland Sea connects Kyushu and another island.

Historically the Inland Sea as transport line served four coastal areas: Kansai, Chugoku, Shikoku and Eastern Kyushu. The Inland Sea provided each of those regions with local transportation and connected each region to the others and far areas including the coastal area of Sea of Japan, Korea and China. After Kobe port was found in 1868 to serve foreign ships, the Inland Sea became one of major international waterways as connection to the Pacific.

Due to development of land transportation, the transportation between the east and the west, that is, transportation within Shikoku, within Honshu and between Honsyu and Kyushu shifted to railroad and road transport. Two coastal railways, San'yō Main Line in Honshu and Yosan Main Line were built. Those railway lines stimulated the local economy and once invoked a rail mania. Many short railroads were planned to connect a certain station of those two lines and a local seaport on the Inland Sea, and some of them were really built. The Ministry of Railroads, nowadays Japan Railway ran some train ferry lines between Honshu and Shikoku including the line between Uno Station (Tamano) and Takamatsu. When the Great Seto Bridge was finished and began to serve two coastal area, that ferry line was abolished.

Major tourist sites

The coastal area of the Inland Sea is one of most famous tourist destinations in Japan. Even before Japan opened to foreigners in the middle of the 19th century, its beauty was praised and introduced to the Western world by those who visited Japan including Philipp Franz von Siebold, and after its opening, Ferdinand von Richthofen and Thomas Cook.

Its coastal area except Osaka prefecture and adding a part of Wakayama prefecture was appointed the Inland Sea National Park (瀬戸内海国立公園, Setonaikai Kokuritsu kōen) on March 16, 1934 as one of three oldest national park in Japan.

Itsukushima Shrine, in the island town of Miyajima, is a UNESCO World Heritage Site, and is one of the most famous Japanese sites outside of Tokyo and Kyoto. Shodoshima, nicknamed the "island of olives," and the Naruto whirlpool are two more well-known tourist sites. Neighboring locations like Kotohira and Okayama are often combined to the tour of the Inland Sea region. Some historic sites including Yashima (in Takamatsu), Kurashiki also attract many visitors. Hiroshima is the neighbor city to Itsukushima Shrine and another UNESCO World Heritage Site because of A-bomb damage in 1945.

External links


et:Seto de:Seto-Inlandsee id:Laut Pedalaman Seto ja:瀬戸内海 fr:Mer intrieure de Seto


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