The Triads, or Chinese underworld, was founded in the 17th Century by a monk of the Shaolin monastery in order to rid China of her barbarian conquerors. According to the book "Chinese Looking Glass" by Dennis Bloodworth, the TRIAD's use the triangle as their symbol to represent the harmonious blending of Heaven, Earth and Man. Each of these elements also had its own secret number, which was always a multiple of three. They used the number 36 for Heaven, 108 for man and 72 for Earth. These numbers are still respected within the Triads to a point where even the entrance fee paid by new members are $1.80, $3.60, $7.20, or $10.80.
This numbering system comes from early Taoist numerology. In addition the author points out that the Manchus destroyed the Shaolin monastery with the help of a traitor who was Number seven in the Shaolin hierarchy, so that the number seven is never used in Triad rituals. Also eighteen heroes escaped the Shaolin monastery, but after many battles, only five of these survived. These are the five ancestors to whom homage is paid in every Triad lodge. There is a difference of opinion between the Triad version and the martial artist version of who the five monks were.