Centuries: 6th century - 7th century - 8th century
- Emperor Justinian II of the Byzantine Empire defeats the Bulgarians.
- King Caedwalla of Wessex is baptised in Rome and dies ten days later.
688 is also the hull number of the US Navy attack submarine USS Los Angeles. The number has come to be a shorthand reference for all of the many submarines of the Los Angeles class. For instance, 688 Sub Attack is a computer game about submarines.\n