The Octagon (Asṭ ạ konạ , Asṭ ạ̄ ra)
The octagon appears less frequently as a constituent part of yantras and can be formed in several ways. A common method to obtain an octagon is to draw two crossed or intersecting squares. The symbolism of the octagon, like that of the eightpetalled lotus, is connected with the eight directions.
Like maṇḍalas, yantras frequently feature a lotus
design. Depending on the context, different interpretations
of the lotus design and the lotus petals
have been offered. The symbolism of the lotus is
discussed above in connection with maṇḍalas.
One circle or three concentric circles frequently
surround the inner structure of yantras.
The Outer Square
The circle or circles in a yantra are usually surrounded
by an outer square, which often consists
of three nested squares. The square, which also
appears close to the outer edge of maṇḍalas, is called
“earth house” (bhūgṛha), “earth city,” or “earth
citadel” (bhūpura), since the square is a symbol of
the earth. Among the symbolic shapes of the elements,
a (yellow) square represents the earth. The
symbolism of the square is connected with that of
the number four and the four cardinal directions.
The square has a T-shaped gate (dvāra) in each
cardinal direction. Like the sides of a square, the
gates are equated with groups of four. Pāñcarātra
Saṃhitās interpret the three nested squares of the
outermost square as sattva, rajas, and tamas. This
interpretation is also attested for the three nested
squares of the outer square formation of the
bhadramaṇḍalas of the Smārta tradition, which
are white, red, and dark, symbolizing the three
constituents (guṇa) of primary matter (prakṛti) in
the Sāṃkhya system.