The year 688 BC was a year of the pre-Julian Roman calendar. In the Roman Empire, it was known as year 66 Ab urbe condita . The denomination 688 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

• Traditional date for the founding of Gela in Sicily by colonists from Rhodes and Crete.^[1]

• Greece's games of the 23rd Olympiad are held at Olympia; boxing is added to the Olympic Games that are more and more intended as preparation for war.