“This is Flame Barrel... The fire dragons' graveyard. It's where the fire dragons who've degenerated into savage beasts come to wait for their death.”
During Marth's journey along Anri's Way to find Falchion, he is joined by a guide, Xane. They pass through the Flame Barrel on their journey, whereupon Xane describes the area's history as well as the nature of degenerated dragons.
According to Xane, the Flame Barrel is where degenerated Fire Dragons go to await their death. In the area, the local "fire clans" that rule the valley somehow manipulate and degrade the insane dragons into working for them like beasts of burden. They use the dragons as weapons of war against Marth's party, though Marth defeats all of them and obtains a Starsphere Shard in the process.
It is here that Marth encounters Darros the pirate.