The wide and open regions of Lothlann, Maglor's Gap, Thargelion, and the Ossiriand made up the majority of the East Beleriand. They were lands consisting mostly of hills and lowlands with dense forests, scattered woodlands, scrubs, stunted trees, and thickets. Climates varied from severely cold and dry winters with short and cold summers, to mild winters with mild summers. All of which were under the influence of the cold and dry winds from Dor Daidelos and the Iron Mountains to the north, and the warm and moist winds coming from the sea.
Before the Return of the Ñoldor, the areas of the East Beleriand were inhabited by the Laiquendi (Green-elves) living in the Ossiriand and the Sindar in other parts. When the Ñoldor did return, the majority of the region was under control of Maedhros, Maglor, Celegorm, Caranthir, Curufin, Amrod and Amras, the Sons of Fëanor. They built extensive fortresses and Castles in the area between Lothlann and Thargelion which buttressed Morgoth's domain in the farther north. The dominant languages here during this time was Sindarin and Quenya but later there were also mannish speeches as well.
By the later First Age, more and more of this land fell under the power of Morgoth until it was finally conquered by the Dark Powers and was renamed Dor Daedeloth. It, along with the rest of Beleriand, was destroyed after the War of Wrath. However, some of it did survive into the Second and Third Ages becoming Lindon, the land of Gil-galad and then Círdan the Shipwright.
- East Beleriand at the Encyclopedia of Arda