Given the task definition and input, reply with output. Generate a question which can yield the answer mentioned in the input. Generated question must be answered by the answer provided in input, without using any extra knowledge.

Context : The Battle of Navarino was a naval battle fought on 20 October 1827, during the Greek War of Independence (1821--32), in Navarino Bay (modern-day Pylos), on the west coast of the Peloponnese peninsula, in the Ionian Sea.
Answer : 20 October 1827
When did Battle of Navarino occur?