Ever heard of caltrops? Me, I love learning about history, but even still, this was a new one for me. In case you're in the same boat, they're what the website medievalbritain.com refers to as "medieval area-denial weapons," and that's because of two things.
One is that, no matter how you throw them, there will always be at least one sharp spike pointing upward. And two is that, no matter what unfortunate creature or vehicle steps or rolls over the protruding, sharp spikes, they're most assuredly going to have a very bad time.
