It was said to have shown the Trinity, while others likened it to the Mitre of Saint Peter. The symbolism of the triangle is part and parcel of that of the number three and can only be separated from it in terms of its relationship with other geometrical figures. According to Boethius, who adopted the Platonists' geometrical theories studied by Latin writers, the primary plane surface is the triangle, the second the square and the third the pentagon. If lines are drawn from its centre to its angles, any figure may be divided into several triangles. The triangle is the foundation upon which the pyramid is built.
Equilateral triangles symbolize the godhead, harmony and proportion.
Since all procreation proceeds from division, humans correspond to an equilateral triangle split into two, that is, with a right-angled triangle. Plato, in the Timaeus, considers that the latter also stands for the Earth. Its connections with the Sun and with maize made the triangle doubly a fertility symbol. In India, Greece and Rome, triangles were often used as decorative motifs in friezes. Their significance would seem always to have remained the same.