>The jury is mainly a common law institution.
Medieval court records are as much fun to read as our own court transcripts. This is from London, July 17, 1298. The jury was fined for giving a false verdict.
Arnald Vylote, a foreigner, was forbidden to sell wine retail and to act as a lodging-house keeper for foreigners, unless he received special permission.
Aveswote was attached to answer the Commonalty on charges of being a foreign lodging-house keeper, buying Ryns wine from foreigners and selling it retail to foreigners and citizens, and allowing foreigners in her house to deal in ginger, woad, cloth and other merchandise, which they sent over the water by night, thus defrauding the Sheriffs of their customs. The defendant admitting buying and selling the wine, but pleaded a licence from Sir Ralph de Sandwych, then Warden of London, and Elyas Russel, then Sheriff (fn. 2) , who gave her leave to do so because there was no Assize of such wine at the time. She denied harbouring foreigners except her brother and the son of her uncle, or that she allowed buying and selling in her house. A jury of the venue of Ebbegate brought in a verdict that she had bought and sold wines, as she admitted, and that she harboured many more foreigners than her brother and her uncle's son, but whether they were kinsmen the jurors did not know; and also that she sold foreign woad retail to foreigners in her house. She was mainprised by Thomas Juvenal and John de Wengrave to come up for judgment on Wednesday. As the jurors afterwards repudiated their first verdict that she sold woad retail, and acquitted her of this charge, judgment was given that all the jurors be amerced for a false verdict, viz. William de Paris and his fellows as appears on the panel.
http://www.british-history.ac.uk/report.asp?compid=31967#s5