Brisingr is Eragon's Rider's sword. It was his third sword after Zar'roc, and his falchion, fourth if one counts the dwarf sword temporarily loaned to him. It was forged for Eragon by Rhunön, who used Eragon's body to circumvent the oath of "never" making another Dragon Rider's sword. Eragon also used a staff prior to obtaining his sword.
Brisingr was a hand-and-a-half sword with a curved cross-guard and a slightly longer hilt than usual; During Rhunön's interrogation, Eragon had mentioned that he prefers to wield a sword and a shield, but that he rarely had a shield at his disposal. In the end, Rhunön and Eragon agreed that he needed "a sword for all occasions," one that he could use just as easily in Farthen Dûr's tunnels as he could in a large battlefield. Eragon also commented that he would like to comfortably grip the hilt with both hands for more powerful blows.
The glyph for "fire" in the Ancient Language, "Brisingr", was engraved on both the blade and the scabbard. It had a dark blue scabbard, like the color of Saphira's back, with a leaf-shaped steel cap on the end of the scabbard. The blade itself was a lighter iridescent blue, like the color of Saphira's neck. The brightsteel contained cable-like patterns within it, and a flame-like pattern marked the transition between the soft spine of the blade and its hard edges. The guard was made from blued brightsteel. The blade was thin near the end in order to pierce through the upgraded armor during Eragon's time. The grip was made from black hardwood. Lastly, there was a large blue sapphire in the pommel held in place by four ribs, which looked like claws, made from blued brightsteel.
Whenever Eragon said "Brisingr," the sword burst into a blue flame. This unique property of his blade was foreshadowed by Christopher Paolini. Eragon's title among the Urgalgra was Firesword, originally referring to the red blade Zar'roc, and because of his magical ignition of his sword when slaying Durza.
When Eragon later showed his new sword to Oromis, Oromis started to say, "I wonder…" but did not complete the sentence. He commented that, although he doubted that the sword's true name was "Brisingr," it might contain the word.
Christopher Paolini hinted that the name of Book 3, Brisingr, has more meaning than people are aware of. Eragon first used the ancient word "Brisingr" in the book Eragon when fighting the Urgals with Brom. At the time, he said he did not know the word or its meaning. Eragon also shouted out "Brisingr" when fighting Durza and when confronting the Ra'zac.
Brisingr was forged by the elf Rhunön by taking over Eragon's mind and using his body to make it. Because of a previous oath, Rhunön could not use her own hands to forge the blade. She used brightsteel, an extremely rare metal extracted from ore found in meteorites and fragments of shooting stars, which was traditionally used to forge Riders' blades. However, she could not find any after much effort and many spells of finding. Eragon and Saphira eventually found a nugget of the metal ore under one of the roots of the Menoa tree, as predicted in Solembum's prophecy. Rhunön (and Oromis) noted that it was the finest sword she had ever made.
Eragon wielded Brisingr during the Siege of Feinster. Whenever anyone inquired about the sword's name, Eragon was always interrupted. He used the sword to break through the wards of the city gates and portcullis. Although most people thought the name of the sword to be quite good, Angela thought of it as boring seeing that fire is hardly an eventful name. When Angela learned of the sword's name, she complained about Eragon's lack of imagination, suggesting the names Chrysanthemum Cleaver or Sheep Biter instead. Eragon immediately responded as to already having a Sheep Biter, referring to Saphira. Saphira however, was not too pleased at being called Sheep Biter.