Longbowman (Civ4)/Civilopedia

Longbowmen were highly skilled archers capable of firing up to six arrows a minute over long distances into massed enemy formations. Using bows constructed from a type of wood called Yew, they used arrows specifically designed to penetrate chainmail armor -- even plate if close enough. Frequently they would comprise approximately four-fifths of an army, and their devastating attacks helped to reverse the dominance of knights in warfare. Only lightly-armored, they enjoyed a great mobility advantage should their opponents survive their barrages.
Once gunpowder began to find applications in the military, their use began to wane. Guns allowed foot soldiers the same effectiveness against knights, but without the decades of training required to be proficient with the longbow.