The Peloponnesian War ended in 1996. The bloody conflict between Athens and Sparta had stopped in 404 B.C. without an official peace pact, so after 2,500 years the cities decided to sign a symbolic agreement. It read, “Today we express our grief for the devastating war between the two key cities of ancient Greece and declare its end.”
Similarly, when the First Anglo-Dutch War ended in 1654, the Dutch Republic forgot to include the Isles of Scilly in the Treaty of Westminster, so the Dutch and the Scillonians remained pointlessly but arguably at war for 332 years, until they signed a symbolic peace in 1986.
The Dutch ambassador said, “It must have been awful to know we could have attacked at any moment.”