Three: A Special Number for the Celts
The Celts believed that certain numbers were associated with various aspects of existence. Three is one of those numbers. Consequently, sets of 3 can be found throughout Celtic culture. For instance, the interrelationship of land, water, and air was considered to be essential to existence. Not surprisingly then, the earth/sky/water were considered to be a three layered marriage.
Three appears in many other contexts....harvesting, planting, and fallowing....mother, maiden, crone (grandmother)....father, son, grandson. The significance of the "three" at issue depends upon the context in which it is found. For instance, a three fold symbol found in a smithy's workshop most likely represents the interconnectedness of harvesting, planting, and fallowing.
A considerable amount of celtic jewelry use three as their organizing principle. One such design can be seen by following this link: https://www.shanore.com/sterling-silver-trinity-stone-set-necklace-produ...