What did the cannonball say to the castle wall?

This classic bit of historical humor relies entirely on some clever wordplay, specifically a pun on the phrase "breakthrough." When a cannonball declares its intentions, it's literally planning to smash its way through the physical barrier of a castle wall. But "making a breakthrough" also colloquially means achieving a significant discovery or advancement, often after overcoming a challenge.

Historically, the invention and deployment of cannonballs were indeed a massive "breakthrough" in siege warfare. Before their widespread use, castles were formidable strongholds, often requiring lengthy and costly sieges to overcome. The sheer destructive power of a cannonball, designed to batter down stone, completely revolutionized military tactics and made many traditional castle defenses obsolete.

So, the joke playfully gives the cannonball a boastful, almost human ambition, combining its literal destructive purpose with the figurative sense of making a monumental impact. It’s a heavy joke with a very light touch, perfectly encapsulating both the physical force and the historical significance of these metallic projectiles.