The term “Seven Seas” appears as early as 2300 BC in Hymn 8 of the Sumerian Enheduanna to the goddess Inanna, but it’s not so clear which bodies of water were intended. It depends on the size of the known world.
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.
A history of Venice states:
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.
This passage demonstrates the Seven Seas as referenced in Medieval Arabian literature: the Persian Gulf (“Sea of Fars”), the Gulf of Khambhat (“Sea of Larwi”), the Bay of Bengal (“Sea of Harkand”), the Strait of Malacca (“Sea of Kalah”), the Singapore Strait (“Sea of Salahit”), the Gulf of Thailand (“Sea of Kardanj”), and the South China Sea (“Sea of Sanji”).
- the Adriatic Sea
- the Mediterranean Sea, including its marginal seas, notably the Aegean Sea.
- the Black Sea
- the Caspian Sea
- the Persian Gulf
- the Arabian Sea (which is part of the Indian Ocean)
- the Red Sea, including the closed Dead Sea and the Sea of Galilee
In Colonial times the Clipper Ship Tea Route from China to England was the longest trade route in the world. It took sailors through seven seas near the Dutch East Indies: the Banda Sea, the Celebes Sea, the Flores Sea, the Java Sea, the South China Sea, the Sulu Sea, and the Timor Sea. The Seven Seas referred to those seas, and if someone had sailed the Seven Seas it meant he had sailed to, and returned from, the other side of the world.
One modern geographical classification scheme counts seven oceans in the world: The North Pacific Ocean, the South Pacific Ocean, the North Atlantic Ocean, the South Atlantic Ocean, the Indian Ocean, the Southern Ocean, and the Arctic Ocean. Oxford University Press‘ online dictionary defines “the seven seas” as “all the oceans of the world (conventionally listed as the Arctic, Antarctic, North Pacific, South Pacific, North Atlantic, South Atlantic, and Indian Oceans).”