Seven seas

The "Seven Seas" (as in the idiom "sail the Seven Seas") is an ancient phrase for all 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 "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.

In the 9th century AD, author Ya'qubi wrote:

Whoever wants to go to China must cross seven seas, each one with its own color and wind and fish and breeze, completely unlike the sea that lies beside it. The first of them is the Sea of Fars, which men sail setting out from Siraf. It ends at Ra’s al-Jumha; it is a strait where pearls are fished. The second sea begins at Ra’s al-Jumha and is called Larwi. It is a big sea, and in it is the Island of Waqwaq and others that belong to the Zanj. These islands have kings. One can only sail this sea by the stars. It contains huge fish, and in it are many wonders and things that pass description. The third sea is called Harkand, and in it lies the Island of Sarandib, in which are precious stones and rubies. Here are islands with kings, but there is one king over them. In the islands of this sea grow bamboo and rattan. The fourth sea is called Kalah and is shallow and filled with huge serpents. Sometimes they ride the wind and smash ships. Here are islands where the camphor tree grows. The fifth sea is called Salahit and is very large and filled with wonders. The sixth sea is called Kardanj; it is very rainy. The seventh sea is called the sea of Sanji, also known as Kanjli. It is the sea of China; one is driven by the south wind until one reaches a freshwater bay, along which are fortified places and cities, until one reaches Khanfu.

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Wikipedia