The Baltic Sea (German: Ostsee) is located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and the Little Belt. The Kattegat continues through the Skagerrak into the North Sea and the Atlantic Ocean. The Baltic Sea is artificially linked to the White Sea by the White Sea Canal and to the North Sea by the Kiel Canal.
At the time of the Roman Empire, the Baltic Sea was known as the Mare Suebicum or Mare Sarmaticum. Tacitus in his AD 98 Agricola and Germania described the Mare Suebicum, named for the Suebi tribe, during the spring months, as a brackish sea when the ice on the Baltic Sea broke apart and chunks floated about. The Suebi eventually migrated south west to reside for a while in the Rhineland area of modern Germany, where their name survives in the historic region known as Swabia. The Sarmatian tribes inhabited Eastern Europe and southern Russia. Jordanes called it the Germanic Sea in his work the Getica.
Since the Viking age, the Scandinavians have called it "the Eastern Lake" (Austmarr, "Eastern Sea", appears in the Heimskringla and Eystra salt appears in Sörla þáttr), but Saxo Grammaticus recorded in Gesta Danorum an older name Gandvik, "-vik" being Old Norse for "bay", which implies that the Vikings correctly regarded it as an inlet of the sea. (Another form of the name, "Grandvik", attested in at least one English translation of Gesta Danorum, is likely to be a misspelling.)
In addition to fish the sea also provides amber, especially from its southern shores. The bordering countries have traditionally provided lumber, wood tar, flax, hemp, and furs. Sweden had from early medieval times also a flourishing mining industry, especially on iron ore and silver. Poland had and still has extensive salt mines. All this has provided for rich trading since the Roman times.
In the early Middle Ages, Vikings of Scandinavia fought for control over the sea with Slavic Pomeranians. The Vikings used the rivers of Russia for trade routes, finding their way eventually to the Black Sea and southern Russia. Lands next to the sea's eastern shore were among the last in Europe to be converted into Christianity in the Northern Crusades: Finland in the twelfth century by the Swedes, and what are now Estonia and Latvia in the early thirteenth century by the Danes and the Germans (Livonian Brothers of the Sword). The powerful German Teutonic Knights gained control over most of the southern and eastern shore of the Baltic Sea, while fighting the Poles, the Danes, the Swedes, the Russians of ancient Novgorod, and the Lithuanians (the last Europeans to convert to Christianity).
Later, the strongest economic force in Northern Europe became the Hanseatic league, which used the Baltic Sea to establish trade routes between its member cities. In the sixteenth and early seventeenth centuries, Polish-Lithuanian Commonwealth, Denmark and Sweden fought wars for Dominium Maris Baltici ("Ruling over the Baltic Sea"). Eventually, it was the Swedish Empire that virtually encompassed the Baltic Sea. In Sweden the sea was then referred to as Mare Nostrum Balticum ("Our Baltic Sea").
In the eighteenth century, Russia and Prussia became the leading powers over the sea. Russia's Peter the Great saw the strategic importance of the Baltic and decided to found his new capital, St. Petersburg at the mouth of the Neva river at the east end of the Gulf of Finland. There was much trading not just within the Baltic region but also with the North Sea region, especially eastern England and the Netherlands: their fleets needed the Baltic timber, tar, flax and hemp.
During the Crimean War, a joint British and French fleet attacked the Russian fortresses by bombarding Sveaborg, which guards Helsinki; Kronstadt, which guards St. Petersburg; and by destroying Bomarsund in the Åland Islands. After the unification of Germany in 1871, the whole southern coast became German. The First World War was partly fought in the Baltic Sea. After 1920, Poland returned to the Baltic Sea, and the Polish ports of Gdynia and Gdańsk became leading ports of the Baltic.
During the Second World War, Germany reclaimed all of the southern shore and much of the eastern by occupying Poland and the Baltic states. In 1945, the Baltic Sea became a mass grave for drowned people on torpedoed refugee ships. The sinking of the Wilhelm Gustloff remains the worst maritime disaster, killing (very roughly) 9,000 people. In 2005, a Russian group of scientists found over five thousand airplane wrecks, sunken warships, and other materiel mainly from the Second World War, lying at the bottom of the sea.
After 1945, the sea was a border between opposing military blocks: in the case of military conflict in Germany, in parallel with a Soviet offensive towards the Atlantic Ocean, communist Poland's fleet was prepared to invade the Danish isles.
Since May 2004, on the accession of the Baltic states and Poland, the Baltic Sea has been almost entirely surrounded by countries of the European Union (EU). The only remaining non-EU areas are the Russian metropolis of St. Petersburg and the Kaliningrad Oblast exclave.
Winter storms begin arriving in the region during October. These have caused numerous shipwrecks, such as the sinking of the ferry M/S Estonia en route from Tallinn, Estonia, to Stockholm, Sweden, in 1994, which claimed the lives of hundreds. Older, wood-based shipwrecks such as the Vasa tend to remain well-preserved, as the Baltic's cold and brackish water does not suit the shipworm.