River Sirion

The greatest of the rivers of Beleriand, the Sirion flowed some 850 miles from its source in the cold highlands of the Ered Wethrin to its mighty delta on the Bay of Balar. It was unusual in that, for some nine miles of its middle course, it flowed underground from the wide, enchanted marshland of Aelin-uial beneath the high land known as the Andram. The Sirion was regarded as the border between East and West Beleriand.