More important it is a boundary of concentrated power. Within the circle you are able to transcend the physical and open your mind to a higher level of consciousness. In ancient times circles were drawn around sick people to protect them against demons. The circle was also used in ancient Pagan rites. The circle serves to keep out unfriendly spirits.
Negative energy is cleared prior to casting a circle.
The circle should be nine feet in diameter but larger circles are sometimes cast for large groups. The alter and ritual tools are placed inside the circle. The circle is drawn on the ground or sometimes laid out with a cord. The witch visualizes a field of energy. The working space of the circle is in fact a three dimensional sphere.