Where was direct democracy first used?

The usual answer is "Athens" in ancient Greece, but in reality the first examples date back much further, to even prehistoric times. Even in the most primitive tribes the men used to elect - especially when fighting had to be done - a strong and clever warrior to lead them into battle. Which is - in all its simplicity - an example of 'direct democracy'.

The idea that we have about Athens' democracy is mostly the product of British poet Alfred Lord Tennyson's writings in the 19th century. He was a fierce supporter of Greece when it fought a war of independence against Ottoman Turkey. He (very succesfully, too) drummed up support for Greece by Britain and France by labeling Greece 'the birthplace of democracy'. In reality, all ancient Greek cities, including Athens, were olichargies from beginning to end. Athens for a while had mass meetings on a limited number of subjects - and just as in many other societies, choosing a war leader was a major one. But the people never got to elect any peacetime leaders (the ruling families saw to that) and Athens never had any democratic institutions.

Ancient Rome is probably a much better choice as an answer. The Roman tribes were regularly called upon to elect public officials and they had a high elected official - a "Tribune of the Plebs" - of their own to protect them agains misuse of power by the Patricians and who even could draft and submit laws.