Crossbow

"It's very compact and light. [...] The advantage it has over a gun is that it's more or less silent."

- Leonardo da Vinci, regarding his crossbow.

The crossbow was a long-ranged weapon, consisting of a bow mounted on a stock, which shot arrow bolts. It could also be used in defensive close-quarters combat.

Unlike the longbow, it could be aimed and fired with a single hand.

High Middle Ages
Altaïr Ibn-La'Ahad used a standard crossbow, despite its usage being uncommon in Europe and the Middle East during the time of the Third Crusade.

Renaissance
The crossbow was a ranged weapon that Ezio Auditore da Firenze could purchase for 12,800 florins, at any of the blacksmiths in Rome. After purchasing the weapon, the carrying capacity of the bolts could be upgraded, by buying the medium and large quivers from tailor shops.

Each crossbow quiver increased the maximum number of bolts carried by five, with the standard number of bolts being fifteen and the maximum number available being twenty-five.

The large crossbow quiver could not be purchased, and required the completion of the Pulling Threads shop quest for the tailor of Tiber Island.

Stealth
The crossbow was a silent but slightly weaker equivalent to the Hidden Gun, and the way the crossbow was fired was similar to that of the Hidden Gun, though it could be aimed quicker, and could be used while freerunning.

Unlike the Hidden Gun, which alerted any nearby guards the moment it was fired, the crossbow only called attention to Ezio after his target fell.

Combat
Alongside its stealth capabilities, the crossbow could be used in open combat. In battle, it could be fired at close range, and could be used to counter an enemy's attack. When fired at point blank, the crossbow would kill the targeted enemy immediately, but the user would be forced to spend a few seconds reloading the weapon.

Crossbowmen and heavy horsemen used the crossbow in battle, both from close and long range. Ezio could also use the crossbow to defend against charging horsemen, by blocking them with the crossbow stock.

Trivia

 * A crossbow was planned to be one of Altaïr's weapons in early designs of Assassin's Creed, but it was removed from the final game due to historical inaccuracies. The crossbow did, however, feature in the E3 trailer and the game's video introduction, showing that it was removed from the game at quite a late date.
 * Despite historical inaccuracies, the crossbow was featured in the first of Altaïr's recorded memories in Assassin's Creed: Revelations, as the weapon used by Haras to kill Assassin hostages.
 * The crossbow was featured in the mobile version of Assassin's Creed, a historical mistake by the developers. The crossbow could be used to kill enemies at a safe distance, to trigger gear mechanisms, or to shoot down flame-holders to light torches. The ammunition of the weapon could be refilled by walking into a weapon recharge point.
 * Ezio Crossbow 1.png an E3 conference trailer, and in certain pre-release images, Ezio was seen equipped with a different crossbow to the one in Assassin's Creed: Brotherhood. This particular crossbow had the same design as the ones used by Crossbowmen guards.
 * Sometimes, when Ezio performed one of the possible counterattacks with the crossbow, the firing sound would not occur.
 * During the Animus loading screen, if Ezio drew his crossbow, a single crossbow bolt could be found lying on the ground, though it disappeared when the crossbow was put away.
 * When performing certain actions with the crossbow, Ezio's upper body did not move at all. This gave Ezio a robotic appearance when running, as his entire upper body was completely still while performing any actions.
 * In Assassin's Creed: Revelations, it took more than one crossbow bolt for Ezio to kill a Byzantine Almogavar or an Ottoman Janissary; though Assassin apprentices could kill them with one bolt.