River Running

Celduin (The River Running) was a long river that flowed from the Lonely Mountain, through the Long Lake and down to the inland sea of Rhun. It formed the border of Wilderland and Rhun, and was used as a trade route between Erebor, Dale, Lake-town and Dorwinion.
The birthplace of the River, within the bowls of Erebor, also supplied water for the Great Forges of the underground realm, while the river itself, crossing in front of its gate, served as a moat.
During the Siege of Erebor, Thorin had the bridge over the river smashed. The ruins blocked the stream, causing the river to overflow before the cold of the approaching winter made it freeze. The frozen river was used by Fili, Kíli, Balin and Dwalin, riding an Iron-hill war chariot, as a route to get to Azog's command post on Ravenhill during The Battle of the Five Armies, where they were nearly stopped by Trolls and Wargs.