Moshio, literally seaweed-salt (mo- meaning seaweed, -shio meaning salt), is known to be the origin of salt making in Japan.
The Inland Sea (Setonaikai) area was a famous salt production region since the 9th century due to its warm climate, but it is the Kamagari region in Hiroshima prefecture that is known to have first produced salt as early as the Kofun period (ca. late 3rd - 7th century). Back then a method called "moshio-yaki", literally moshio firing, was used in making salt.
Beige in color, moshio is salt abundant in mineral such as iodine (a compound found in seaweed), calcium, potassium, magnesium, etc. And because its low in salt content, moshio helps control excessive consumption of sodium. Mild taste of moshio is a result of the umami extracted from seaweed, a unique quality of moshio.
There are only two ingredients in making the moshio: sea water of Setonaikai (the Inland Sea, Japan) and sargassum (brown seaweed).