A hand-and-a-half sword is a long straight-bladed sword renowned for being lightweight, yet powerful, and able to pry open plate armor. The swords are versatile and effective in battle because they could be wielded with two hands, yet a fighter could also wield it with one hand if they fought using a shield or another weapon. The advantage of the hand-and-a-half sword was that it could be used for stabbing like a normal sword and dealing sweeping critical blows like a longsword. It also enabled the user to use whatever fighting style he/she prefers with little hindrance. The hand-and-a-half sword was a devastating weapon in the hand of a skilled warrior or dragon rider.
Most hand-and-a-half swords have simple "cruciform" hilts. The term "hand-and-a-half" have originated due to the fact that the sword was designed for both one and two-handed use, not because one and a half hands are needed to wield it. A hand-and-a-half sword can be anywhere from 3.5 to 4.5 feet long and generally weighs around 2-4 pounds.
Use in the Inheritance cycle
Murtagh used a hand-and-a-half sword with a leather-wrapped hilt (though the detail of the hilt is not mentioned until Brisingr) throughout his travels with Eragon, up until he claimed Zar'roc from Eragon at the Battle of The Burning Plains. Eragon kept Murtagh's old sword as a memento after the battle, though he did not use it for himself.
Eragon's new sword, Brisingr, was also designed as a hand-and-a-half sword. This was an interesting twist because Eragon and Murtagh are half-brothers.