The River Sirion was created in the Battler of the Powers, when the Valar fought the armies of Morgoth in the North. The battle was so tremendous that it altered the geography of Arda, which led to the creation of the River Sirion in Beleriand. The river starts from the slopes of Ered Wethrin, and flows from north to south. It sources is marked at Eithel Sirion, it flows to the Fen of Serech, in between Ered Wethrin and Crissaegrim, and then it splits the Forest of Brethil from the greater part of Doriath where it merges with the River Mindeb, River Teiglin, and the River Esgalduin. At the southern reaches of the Forest of Region, it merges with the River Aros, which form the Fens of Sirion that pass under Andram. Sirion emerges again at the Gates of Sirion and then flows further south through Nan-Tathren, where it merges with the River Narog. Then it shapes into a delta at the Mouths of Sirion as it flows into the Bay of Balar.