Robinson Crusoe

When he saw the approaching canoes, Crusoe stayed in his castle and prepared for an attack..... just in case.

From the text:

I was surprised one morning by seeing no less than five canoes all on shore together on my side the island, and the people who belonged to them all landed and out of my sight. The number of them broke all my measures; for seeing so many, and knowing that they always came four or six, or sometimes more in a boat, I could not tell what to think of it, or how to take my measures to attack twenty or thirty men single-handed; so lay still in my castle, perplexed and discomforted. However, I put myself into the same position for an attack that I had formerly provided, and was just ready for action, if anything had presented.