The River Running was a 600-Númenórean miles long river that poured out of the gate of the Lonely Mountain, ran south through the Long Lake and thence through the eastern outskirts of Mirkwood, then south east through apparently uninhabited regions of Rhovanion to its confluence with the Carnen and finally in a long south-eastward loop to the great inland Sea of Rhûn, past the land of Dorwinion.
The Celduin had three tributaries: the Forest River, which flowed into the Long Lake from the west; a small unnamed river that flowed from the Mountains of Mirkwood to join the Celduin just north of the Old Forest Road; and the Carnen, which entered the Celduin from the northeast about halfway between Mirkwood and the Sea of Rhûn.
In the thirteenth century of the Third Age the Celduin had formed the northeast border of the lands of Vidugavia. During the Great Plague of T.A. 1636 more than half of the people of Rhovanion died and when the Wainriders invaded from the east (beginning in 1851) the remaining Northmen in the region fled across the Celduin and merged with the folk of Dale. After the threat of the Wainriders ended some of the Northmen drifted back along the banks of the Celduin but when Cirion became the Steward of Gondor he learned that new Easterlings were again driving the remnant of the Northmen up the Celduin.
Between the time when Thráin I founded the dwarf-kingdom in the Lonely Mountain (in 1999) and the arrival of Smaug (in 2770) the Northmen living between the Celduin and Carnen grew strong and repelled all eastern enemies. Even after the arrival of the dragon at the Lonely Mountain the Celduin was still a highway of trade for Thranduil's kingdom, the town of Esgaroth, and places to the south.
In none of the maps that showed Rhovanion (in The Lord of the Rings, the Pauline Baynes' Map, or the Unfinished Tales) was it made clear what the name of the river was from the confluence of the Celduin and the Carnen to the Sea of Rhûn. However, in the Index to the Unfinished Tales Christopher Tolkien included information about the Carnen: "'Redwater', river flowing down from the Iron Hills to join the River Running" and the Celduin: "River flowing from the Lonely Mountain to the Sea of Rhûn". Per these statements it was the Celduin that flowed to the Sea and the Carnen was but one of its tributaries.
- ↑ J.R.R. Tolkien, The Hobbit, "Not at Home"
- ↑ 2.0 2.1 J.R.R. Tolkien, The Hobbit, "Map of Wilderland"
- ↑ 3.0 3.1 J.R.R. Tolkien, Christopher Tolkien (ed.), Unfinished Tales, "The West of Middle-earth at the End of the Third Age" [map]
- ↑ Pauline Baynes' Map of Middle-earth (1970)
- ↑ J.R.R. Tolkien, The Lord of the Rings, Appendix A, "The Númenorean Kings", "Gondor and the Heirs of Anárion"
- ↑ 6.0 6.1 6.2 J.R.R. Tolkien, The Lord of the Rings, Appendix B, "The Third Age"
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), Unfinished Tales, "Cirion and Eorl and the Friendship of Gondor and Rohan", (i) The Northmen and the Wainriders
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), Unfinished Tales, "Cirion and Eorl and the Friendship of Gondor and Rohan", (ii) The Ride of Eorl
- ↑ J.R.R. Tolkien, The Lord of the Rings, Appendix A, "Durin's Folk"
- ↑ J.R.R. Tolkien, The Hobbit, "A Warm Welcome"
- ↑ J.R.R. Tolkien, Christopher Tolkien (ed.), Unfinished Tales, Index