The root of the word “trivial”

Today, I came across the seven liberal arts (artes liberales in Latin) which were the basis for the education of students in the middle ages. They are:

- grammar
- rhetoric
- dialectic

and

- arithmetic
- astronomy
- geometry
- music

The seven disciplines were divided into the three verbal arts known as the trivium (means: “the threefold way”), and the four other subjects that were known collectively as the quadrivium.
I can now understand easily why something is called trivial.