Sword of Altaïr

Throughout the events of Assassin's Creed, Assassin's Creed: Altaïr's Chronicles, and Assassin's Creed: Bloodline, the Assassin Altaïr Ibn-La'Ahad wielded a personal sword of superior power compared to all other weapons. The sword continues its appearence in Assassin's Creed II, and Assassin's Creed: Brotherhood, where it is named, the "Sword of Altaïr". However, it is now used by Ezio Auditore da Firenze, a descendant of Altaïr. The blade's guard is shaped like an eagle's wings and the bottom of the hilt has the shape of an eagle's head, while the blade itself is both long and agile, making it a light and deadly weapon.

Assassin's Creed
The game starts with Altaïr using the Syrian sword, which he uses with great skill and ease, until Al Mualim demotes him to Novice for breaking all three tenets of The Creed. During his progression back into the higher ranks, he starts off with a basic sword similar to the Sword of Altaïr, though it does not have a cross guard. After he assassinates his four assigned targets, he is granted the use of his personal sword once more. He continues to uses this sword until he is finally given the Syrian sword.

Assassin's Creed: Bloodlines
Altaïr still possesses his sword during the events after Assassin's Creed, in Assassin's Creed: Bloodlines. In fact, his swords can now be found hanging within Kantara Castle's Great Hall (in "The Bull" stage), as ornaments. During the game, this is the only sword available for his use. In the beginning, its attack power is rather low, and enemies have to be struck with it multiple times to be killed. However, upgrades for the sword and other weapons of Altaïr can be purchased by collecting Templar coins.

Assassin's Creed II
Altaïr's Sword is available at the Monteriggioni blacksmith for 50,000ƒ (or less if the store has been renovated) after DNA Sequence 8. This sword is the most powerful melee weapon, as all three stats are maxed out. Ezio wielded this sword when he fought Rodrigo Borgia in the Vault.

Assassin's Creed: Brotherhood
Since Assassin's Creed: Brotherhood takes place directly after Assassin's Creed II, Ezio Auditore was still wielding the sword while he made his escape from the Vatican Vault into Rome with his uncle Mario. During the Siege of Monteriggioni, a cannon ball was shot through his room. As he was sleeping with Caterina Sforza at the time, he was unable to re-equip it, along with most of his armor and other weapons. However, he can re-acquire it by completing all five Assassin's Guild Challenges. Ezio wielded the Sword of Altair during his battle with Cesare in Viana in 1507.

Trivia

 * The guards at Masyaf are seen wielding this sword.
 * It is unknown why the sword is available from the Monteriggioni blacksmith, since the sword (being Altaïr's personal weapon) would be assumed to be available together with his armor once it was unlocked.
 * It is interesting to note that the picture of the weapon's hilt in the blacksmith is wrapped in leather, however, the weapon itself does not have any leather wrapping.
 * After buying the sword, it may occasionally be replaced with the common sword. To properly acquire it if this occurs, simply go to the Villa's weapon rack, and re-equip it.
 * After doing the training exercise in Monteriggioni, Picking Up Weapons, Ezio's sword automatically falls from it's sheath. Using this, then re-equipping the sword from the weapons rack, results in two Swords of Altaïr.
 * The swords appearance is slightly altered in Assassin's Creed II and Assassin's Creed: Brotherhood, with the handle turning from bronzed color, to completely silver.
 * This sword is shorter compared to the other longswords Ezio can use, with the entire sword being only a little longer than the length of his arm. Despite this, Altaïr's sword is still the strongest weapon available.
 * Strangely, though Altaïr's sword is considered the best sword in Assassin's Creed II and Assassin's Creed: Brotherhood, in Assassin's Creed, the Syrian sword (which in Assassin's Creed II was among the cheapest weapons) was the best sword.
 * It is interesting to note that in later memory sequences, if the player has the sword equipped, it is possible to be knocked out of Ezio's hands by Brute guards, and even picked up by an NPC. It can, however, be re-equipped in the Villa or the Tiber Island Hideout, depending on which game is being played.
 * The sword appears on a weapon rack in the Tiber Island Hideout once Ezio completes all five Assassin's Guild challenges, and can only be equipped from there. Just as it did in Assassin's Creed II, it has maximum damage, speed, and deflect stats.
 * Assassin Apprentices are able to use this sword once they reach the final rank of Assassino, however for them, it is called the Assassin Sword.
 * During the memory Follow the Money, in Assassin's Creed: Brotherhood, Ezio kills and impersonates a guard named Luigi in order reach, and infiltrate, Juan Borgia the Elder's party to assassinate him, when a fellow guard draws and raises the Sword of Altaïr to "convince" the senate to hand the chest to Luigi. This is rather unusual, and unclear if intentional or rendered accidentally by the developers.