Originally the
Ancient Greek word for 'assembly', it came to refer to the
jury courts of
Athens, some of the first documented in the world. Previously to the sixth century
BCE, court cases were decided by
magistrates whose power was absolute. Both public
law suits and criminal proceedings went to them, and while some specialized in certain areas or higher prestiged cases like charges of
treason, most took on whatever eclectic cases came about. Things changed when
Solon came to power, however. His
democratic reforms included a clause changing the court system such that rulings of the magistrates could be appealed. Appeals would go to the people assembled as a jury, a court that was given the name
heliaia (also
eliaia, see the node on
Greek for reasons why the 'h' is sometimes dropped). This was an important reform, because previously rampant corruption had made the magistrates a rather standard tool for
oppression.
Although they still retained power, the position of the magistrates was slowly whittled away. Realizing they could get a better hearing in front of a gathering of their peers, and with no obstacles to their objection, many cases were increasingly appealed to be sent on to the heliaia. The work load became heavy enough within thirty years that they had to reject many cases. To solve the problem while keeping in spirit of Solon's new laws, the helialia were divided up into smaller groups that could handle more cases under more specialized areas. The final barrier to full appeal removed, magistrates were relegated to a position of delegation over the jury. They were not as prestigious as today's modern judges, mostly there for form's sake.
Calling all of these smaller courts each a heliaia soon became somwhat cumbersome, so the term dikasteria was developed for them. Heliaia came to refer only to the high court of six jurors (junior archons), which was also called the thesmothetai.
Howatson, M. C. The Oxford Companion to Classical Literature. Oxford: Oxford University Press, 1989.