The Seto Inland SeaThree thousand islands, tidal races, and the families who taxed everyone who passed

The Seto Inland Sea is enclosed between Honshu, Shikoku and Kyushu — roughly 450 kilometres long, shallow, and studded with around three thousand islands. It has been Japan’s main east–west highway for most of recorded history, because moving anything by sea was easier than moving it over mountains.

The tides

Water enters and leaves through a small number of narrow straits, which produces currents that behave like rivers. At Naruto, east of here, the tidal race generates whirlpools several metres across twice a day. At Kurushima the current reverses direction and ships have to time their passage.

That geography is why local knowledge was worth money, and why certain families became extremely powerful.

The Murakami controlled the straits from the fourteenth century, issuing passes, providing pilots, and taking a cut. European visitors called them pirates. They functioned much closer to a coastguard that charged.

The Murakami

Three related branches of the Murakami family held the central straits, based on small fortified islands. They escorted merchant ships, guaranteed safe passage, and destroyed anyone who did not pay. At their height they were a decisive naval force in mainland Japanese warfare.

They were broken up in the 1580s when Toyotomi Hideyoshi banned independent naval power. The Murakami Kaizoku Museum on Oshima, reachable from the Shimanami cycling route, is the place that tells this properly.

And what it looks like now

The calm water, the layered islands and the haze are the reason the Inland Sea is repeatedly described as one of the most beautiful stretches of coast in Asia — it became Japan’s first national park, in 1934.

From a cruise ship you will pass through a large part of it in daylight between Kobe, Takamatsu and Hiroshima. That transit is not filler between ports. It is one of the sights.