This is a hard answer to pin down, because no-one really knows. So this answer is really speculation.
The first person to name it as the Baltic Sea (Mare Balticum) was the 11th century German chronicler Adam of Bremen.
Some claim it might be connected to the Germanic word belt, a name used for two of the Danish straits, the Belts, while others claim it to be derived from Latin balteus (belt). While others believe that it is derived from the Danish baelte, which also means belt.
All we know for certain is that Adam of Bremen describe it as 'Balticus, eo quod in modum baltei longo tractu per Scithicas regiones tendatur usque in Greciam', roughly translates as ' it stretches through the land as a belt.'
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The Baltic Sea
Oresund. The Baltic is between Finland and Estonia, Latvia, and Lithuania
Stockholm is on the coast of the Baltic sea.
The Baltic Sea.
The Baltic sea.
The Baltic Sea. It has amazing beaches in Poland.
baltic sea
They are the Gulf of Bothnia and the Baltic Sea.
The Baltic Sea is a brackish inland sea.
Stockholm is on the Baltic Sea