Conversation so far:
What was the longest battle in the Civil War
the battle of Gettysburg is The largest battle ever fought on the North American continent
How long was the battle of Gettysburg
The epic battle of gettysburg lasted three days
What was the result of the battle of Gettysburg
the battle of Gettysburg resulted in a retreat to Virginia by Robert E. Lee’s Army of Northern Virginia.

Question: what year was the battle
Self-contained rewrite: what year was the Battle of Gettysburg