How To Cast a Circle

In modern Paganism, one of the facets common to many traditions is the use of a circle as a sacred space. While other religions rely on the use of a building such as a church or temple to hold worship, Wiccans and Pagans can cast a circle pretty much any place they choose. This is particularly handy on those pleasant summer evenings when you decide to hold ritual out in the back yard under a tree instead of in your living room!

Bear in mind that not every Pagan tradition casts a circle - many Reconstructionist paths skip it altogether, as do most folk magic traditions.

http://paganwiccan.about.com/od/wiccanandpaganrituals/ht/Cast_Circle.htm