The Seven Seas

The "Seven Seas" (as in the idiom "sail the Seven Seas") is an ancient phrase for all of the world's oceans. Since the 19th century, the term has been taken to include seven oceanic bodies of water:

The World Ocean is also collectively known as just "the sea". The International Hydrographic Organization lists over 70 distinct bodies of water called seas.

The term "Seven Seas" appears as early as 2300 BC in Hymn 8 of the Sumerian Enheduanna to the goddess Inanna. The Mesopotamians were the first in the history of astronomy to keep records of the observed seven moving objects in the heavens – the seven Classical Planets/Seven Heavens – and they made this connection to their seven seas.

Not all Roman uses of septem maria (Latin) would strike a responsive chord today. The navigable network in the mouths of the Po river discharges into saltmarshes on the Adriatic shore and was colloquially called the "Seven Seas" in ancient Roman times. Pliny the Elder, a Roman author and fleet commander, wrote about these lagoons, separated from the open sea by sandbanks:

All those rivers and trenches were first made by the Etruscans, thus discharging the flow of the river across the marshes of the Atriani called the Seven Seas, with the famous harbor of the Etruscan town of Atria which formerly gave the name of Atriatic to the sea now called the Adriatic.

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