Boulder
From King Arthur's Gold Wiki
Boulders are small round rocks that are dispersed in collections whenever bedrock is destroyed. They are also fired from catapults. Each shot launches three boulders at once.
Boulders will damage and possibly kill any players they touch. A knight will get stunned and receive damage from a boulder even if shielded. However, the damage may be reduced by shielding, and it will stop the boulder(s), protecting nearby team mates. Typically, after a boulder is launched, it will bounce several times off of the ground or built structures before rolling to a stop. The boulder will do damage to all blocks except bedrock, and will instantly destroy ladders.