Location - Sea of Fallen Stars
The Sea of Fallen Stars, also known as the Inner Sea, is the largest inland body of water in Faerûn. Its major ramifications include the Dragonmere (Lake of Dragons) on the west, the Dragon and Easting Reaches on the north, the Alamber Sea on the east and the Vilhon Reach on the south. The sea floor is covered with hundreds of shipwrecks.
The name of the sea is from the origin story which states that the Inner Sea formed when the four Inner Seas merged together, coinciding with the loss of entire continents from earthquakes, fires and windstorms due to a star sent by deities to punish the titans’ arrogance. Other theories have sprung up maintaining it was actually the eggs of the first dragons raining down onto the planet.
Tens of thousands of dragon eggs did hatch soon after the event, though the real reason for the destruction was the primordial Asgoroth the World Shaper hurling an ice moon down to Abeir-Toril’s surface.
Sarrukh accounts dated around -31000 DR mention a “changing of the stars” in relation to this event. Few know what this really signified, but the fact is Ao created a clone of Abeir-Toril and sent the new world to another realm, with different stellar cartography.
Regardless, this event, known as the Tearfall caused a climate shift that wiped out the batrachi civilization.
Home to many types of aquatic life, the sea can be quite dangerous. The sea is home to kingdoms of aquatic elves, merfolk and sahuagin. With the exception of a notable violent excursion in 1369 DR, these races rarely interact with the coastal land folk.
The Sea of Fallen Stars has coastlines in many different lands, including Aglarond, Altumbel, Cormyr, Chessenta, Chondath, the Dalelands, Impiltur, Sembia, Mulhorand, Priador, Thay, Thesk, Turmish and Unther.
There are numerous islands in the Sea of Fallen Stars. The Pirate Isles are a group of about sixty rocky islands notable for the concentration of pirate activity that occurs there. Prespur, sometimes known as the Isle of Prespur or the Isles of Prespur, consists of a main island under Sembian control and a smaller unoccupied island called Traitor’s Isle. Alaor is a former Thayan shipyard now under independent rule. The Ship of the Gods is a island volcano in the Alamber Sea. The Whamite Isles are a small chain of islands once ruled by a great Khan.
There is a recognised territorial limit of ten miles (16.1km) offshore amongst all the nations on the Sea of Fallen Stars. Areas of sea further than ten miles from the nearest land are considered neutral territory. Any attacks on shipping within a country’s waters are considered to be acts of war. For most areas these boundaries are clear, but they become more ambiguous in Mulhorand, Thay and Unther due to the continual disputes over borders.
Text from Forgotten Realms Wiki