Caspian Sea
The Caspian has characteristics common to both seas and lakes. It is often listed as the world's largest lake, although it is not a freshwater lake. It contains about 3.5 times more water, by volume, than all five of North America's Great Lakes combined. The Caspian was once part of the Tethys Ocean, but became landlocked about 5.5 million years ago due to plate tectonics. The Volga River (about 80% of the inflow) and the Ural River discharge into the Caspian Sea, but it has no natural outflow other than by evaporation. Thus the Caspian ecosystem is a closed basin, with its own sea level history that is independent of the eustatic level of the world's oceans.
Sea of Azov
The Maeotian marshes around the mouth of the Tanais River (the present-day Don) were famous in antiquity, as they served as an important check on the migration of nomadic people from the Eurasian steppelands. The Maeotians themselves lived by fishing and farming, but were avid warriors able to defend themselves against invaders. Misled by its strong currents, ancient geographers had only a vague idea of the extent of the sea, whose fresh water caused them to typically label it a "swamp" or a "lake". Herodotus (5th-century BC) judged it as large as the Black Sea, while the Pseudo-Scylax (4th-century BC) thought it about half as large. It was long thought to provide direct communication with the Arctic Ocean. Polybius (2nd-century BC) confidently expected that the strait to the Sea of Azov would close in the near future, presumably due to falling sea-levels. In the 1st-century, Strabo reckoned the distance from the Cimmerian Bosporus (the Strait of Kerch) to the mouth of the Tanais at , a roughly correct figure,
but did not know that its width continuously narrows.