Ardhamandala is the fundamental posture of Bharatanatyam. It is also known as Ayatam, Araimandi, Ukkaramandala, or the Half sitting posture. Pure Dance called Nritta involves frequent use of this posture.
In this posture, the performer assumes a half sitting position with the knees turned sideways, and the spine erect. The arms are either extended out or placed firmly on the waist. The dancer is here trying to achieve a series of triangles. The line joining the two shoulders may be conceived as the base of one triangle and the waist as the imaginary apex of an inverted triangle. From this apex a second triangle is conceived with the thighs, as the two sides and the line joining the two knees, as the base of this triangle. The third triangle is formed by the space covered by the two calves and the line joining the two knees. The arms reinforce this by forming other triangles on either side-the extended arm forming one side of the triangle and the line joining the hand to the knee suggesting the second side.
The Natyashastra says that in Ardhamandala, the distance between the head and the navel becomes equal to that between the earth and the navel.