How did motte and bailey castles develop into the stone keep?

Motte and bailey castles evolved into stone keep castles due to the need for greater security and permanence. The original wooden structures were vulnerable to fire and siege, prompting the construction of more durable stone keeps. These stone keeps provided enhanced protection for the lord and his retainers, while also serving as a symbol of power and stability. As warfare evolved, the stone keep became a central feature in the design of medieval fortifications, reflecting advancements in military architecture.