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A mari usque ad mare.
From the sea all the way to the sea.

The motto of the Dominion of Canada; also meaning, "From sea to sea."

In fact, for both Canada and the United States, the "seas" are really oceans. Although the Romans had the word oceanus, which they borrowed from the Greek okeanos; in Homer, it was considered to be a river that surrounded the earth.

The word mare was used more often to mean "ocean". Who could know the difference between oceans, seas, and rivers back in ancient Rome or even in Homer's time? In fact, there are many even in our current existence who can not explain the differences.