From the Tavistock Lectures. 1935

This idea of a receptacle is an archetypal idea. You find it everywhere, and it is one of the central motifs of unconscious pictures. It is the idea of the magic circle which is drawn round something that has to be prevented from escaping or protected against hostile influences.

The magic circle as an apotropaic charm is an archaic idea which you still find in folklore. For instance, if a man digs for a treasure, he draws the magic circle round the field in order to keep the devil out. When the ground-plan of a city was set out, there used to be a ritual walk or ride round the circumference in order to protect the place within.

In some Swiss villages, it is still the custom for the priest and the town council to ride round the fields when the blessing is administered for the protection of the harvest. In the centre of the magic circle or sacred precinct is the temple. One of the most wonderful examples of this idea is the temple of Borobudur in Java.

The walk round, the circumambulatio, is done in a spiral: the pilgrims pass the figures of all the different lives of the Buddha, until on the top there is the invisible Buddha, the Buddha yet to come. The ground-plan of Borobudur is a circle within a square.

This structure is called in Sanskrit a mandala. The word means a circle, particularly a magic circle. In the East, you find the mandala not only as the ground-plan of temples, but as pictures in the temples, or drawn for the day of certain religious festivals. In the very centre of the mandala there is the god or the symbol of divine energy, the diamond thunderbolt. Round this innermost circle is a cloister with four gates. Then comes a garden, and round this there is another circle which is the outer circumference.

The symbol of the mandala has exactly this meaning of a holy place, a temenos, to protect the centre. And it is a symbol which is one of the most important motifs in the objectivation of unconscious images.16 It is a means of protecting the centre of the personality from being drawn out and from being influenced from outside.

Collected Works of C. G. Jung, Volume 18: The Symbolic Life: Miscellaneous Writings;

Para 409-410