From Farnsworth’s Book of Supremely Stumpifying Riddles

Now that autumn has come to Patria we have taken to building great fires in the evenings when we sit together after dinner on the roof of the castle. During these times we like to tell jokes and stories, sing songs, as well as try to stump one another with riddles.

In fact, I’ve taken to writing my own riddles. I’m filling a notebook with them, which I’m planning to publish one day as Farnsworth’s Book of Supremely Stumpifying Riddles. Here’ a sample. When you think you’ve guessed it, leave your answer in the comments box.

I’ve walked every line of battle,

Though I’ve never been to war.

I was there on the Trojan Tub’s sailing,

Though I’ve never left the shore.

I cannot keep from scratching,

As I defeat the mightiest sword.

What am I?