I sort of have a thing for history, and today I’m indulging myself by talking about the history of juries.

Like many other components of our legal system, juries come to us from Merry Olde England. Way back when—and I do mean way back, because we’re talking at least as early as the 12th century—a group of local men would investigate claims and present the evidence under oath to the judge. Essentially they were both prosecutors and witnesses, and they were called presenting juries. This is quite different from our modern concept of jurors as people who initially know nothing about a crime, although presenting juries still exist to an extent in our modern system; today we call them grand juries, and their job is to determine whether enough evidence exists to proceed with a criminal prosecution.

In 1166, in an act called the Assize of Clarendon, King Henry II required presenting juries throughout England. This was part of his effort to standardize the legal system throughout the country and also to ensure he maintained power in a way that wouldn’t piss off his subjects too much. (This was shortly after the Norman Conquest, when not much love was lost between the Anglo-Saxon commoners and the Norman nobility.) It was a clever idea in that it provided local input into prosecutions while still allowing the king-appointed judges to be in charge. The size of juries was already set at twelve men, although the precise reason for this is not certain.

At this point many criminal cases were still tried by the Catholic church using trial by ordeal. The accused would do something dangerous, like carrying a hot iron, and if he wasn’t harmed, it meant God had been protecting him, which indicated he was innocent. But in 1215 Pope Innocent III called the Fourth Lateran Council. Among other things, the council forbade priests from officiating over trials by ordeal.

As it turns out, 1215 was an important year law-wise, because it’s also the year in which Magna Carta was signed. Magna Carta was essentially a peace treaty between King John and a bunch of unhappy barons who’d been at war with him. The charter limited the king’s powers in several respects, and it guaranteed trial by jury—at least for noblemen.

Stripped of the ability to use trial by ordeal and with Magna Carta as a model, the English legal system turned to those presenting juries as a handy way to determine guilt. These new kinds of juries were called petit juries—small juries—and over the years they were invested with a surprising amount of power, including  jury nullification. That’s the power to essentially ignore the law and acquit an guilty defendant when doing so is just.

English colonists brought their legal system to America. And we ran with the idea of juries, maybe due in part to our populist ideals. Today, the US uses juries more extensively than any country in the world—including the UK, which has scaled back on them in several respects. Most countries don’t use juries at all, leaving it to the judge to determine guilt. Here in the US, the laws and rules regarding juries have evolved as well, but in essence juries are an institution that has been in place for a millennium or so.