What is the origin of the idiom "in stone" and when to use it?

The idiom "in stone" has its origin in the idea of inscriptions or engravings on stone surfaces, such as monuments, gravestones, or ancient tablets. These inscriptions are typically long-lasting and not easily altered, which is why they became symbols of permanence. Over time, this concept was adapted into language and used to convey the idea of something being fixed, unchangeable, or firmly established.