Jury duty originally

The original juryman, it should be remembered, was more a witness than a passive judge of right and wrong. Witnesses, as distinct from jurors, were not introduced into regular English law trials until nearly 1500. Any facts which they did not know already the old jurors were supposed to find out for themselves, outside of court, from general information or gossip presumably spread throughout any small community.

(from A History of England and the British Empire)