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 Sahagun (21 December 1808) was a cavalry clash at Sahagun, Spain, in which the British 15th Light Dragoons (Hussars) defeated two regiments of French cavalry during the Corunna Campaign of the Peninsular War.
Answer : 21 December 1808
When did Battle of Sahagun occurr?