Archer

"Shoot! Shoot the flying demon!"

- An archer's response to seeing Ezio in the Flying Machine.

Archers were guards armed with longbows, who patrolled rooftops and watched for possible enemies below. They usually initiated attacks against any intruder they noticed above ground.

Once goaded into personal combat due to an enemy approaching within a meter or so, an archer would cease firing arrows, and draw his sword or mace. Though accurate and deadly from a distance, archers did not pose a serious threat in close combat.

However, large groups of archers were capable of holding off an Assassin, with some attacking from close-range, and others from a distance.

Third Crusade
Archers were stationed on the rooftops of every city, and on top of large wooden structures in the Kingdom. They usually guarded important areas or people, and strictly enforced the city's laws against civilians being up on the rooftops.

Templar archers were not as hostile as those in Acre, Jerusalem or Damascus, and would usually only provoke a fight with Altaïr if the Assassin was already being pursued.

However, as Altaïr had discovered different ways to assassinate targets at the time, he was capable of performing a Ledge Assassination to dispose of any attacking archers.

Renaissance
Archers took advantage of two varieties of ammunition within the Renaissance: ordinary arrows, and fire-tipped ones. Though the former was widely used, the latter was only notably used in three instances: attacking the horse-drawn carriage of Ezio Auditore and Leonardo da Vinci in the Appennine Mountains, and shooting down the Flying Machine both as Ezio infiltrated the Palazzo Ducale and during the Battle for Forlì.

Aside from attacking passing Assassins, archers also hunted down pickpockets or Borgia Messengers, should they cross their patrol.

Rome
In Rome, crossbowmen and arquebusiers, each with more superior weaponry, largely replaced and took on the role of archers. However, unlike archers, they did not possess a close combat weapon alongside their crossbows or rifles. Instead, they would use their weapon to parry blows.

Instead, archers could only be found guarding the Borgia War Machines; attacking the stolen Machine Gun from rooftops, the Naval Cannon from aboard ships, and the Bomber from archer towers.

Upon building his own guild of Assassins, Ezio trained each of his apprentices in archery. Upon his signal, a group of them could fire a flurry of arrows at an indicated target. This action was referred to as an "Arrow Storm."

Trivia

 * In Assassin's Creed, archers of Acre are the only guards that wear hoods.
 * In Assassin's Creed II, two special variations of archers can be found in assassination missions; Elite Archers and Captain Archers, each with trademark headgear and fighting capabilities.
 * Captain Archers are seen in the missions "Honorable Thief" (Venice Assassination Contract) and in the memory "Everything Must Go;" although the archers in the latter mission were actually thieves, who wore their customary head wraps.
 * During the Bonfire of the Vanities, Girolamo Savonarola's lieutenant, the Captain Guard, makes use of multiple archers (alongside Agile guards) to form a deadly ambush.