Greek Letter - Theta


Theta

Theta - wikipedia.org
In its archaic form, Theta was written as: a cross within a circle and later, as a line or point within a circle. According to Porphyry of Tyros, the Egyptians used an X within a circle as a symbol of the soul; having a value of nine, it was used as a symbol for Ennead.
en.wikipedia.org/wiki/Theta
Theta Rhythm