Cauldrons are considered one of the most ancient of cooking vessels and is often the focal point of the Altar. Traditionally, the Cauldron is crafted from cast iron, has a handle and tripod legs, although wood, ceramics or even soapstone may be crafted to create a cauldron in today's modern world. It is a container in which magical transformations take place. They come in all sizes that range from just a few inches in diameter, perfect for an altar to rather large ones that you may see used inside fireplaces and can be feet in diameter.
The cauldron is a symbol of the Goddess and fertility and growth and represents the element Earth.
It is often filled with seasonal flowers on the Altar, used as a container to burn pine and other Yule offerings to welcome back the light at Yule. It is also used as a container to burn parchments, symbols or even to hold charcoal discs and grain incense.
At Samhain, the cauldron is often used for scrying - filling the cauldron with water and studying the surface whilst meditating and allowing the eye focus to soften. Patterns which reveal themselves on the surface of the water are often interpreted by scryers.
With all these uses, you can see why it is a prominent part of the witch's tools!