Sunday is St. Patrick's Day, a day when Irish and non-Irish around the world observe the traditional death date of Ireland's foremost patron saint.

Google gets into the spirit each year, and on Sunday it dedicated an animated Doodle to the Celtic Triskele, an ancient symbol of Irish culture. Derived from the Greek word triskeles, meaning "three legs," the Triskelion dates back to the Neolithic era but didn't gain popularity with Celtic culture until around 500 BC.

The Triskelion – also known as the Triple Spiral – features three interlocking spirals positioned to appear in constant motion, moving outward from the center. The action of the Triskelion's three spirals is often thought to reflect cycles, progress and revolution.   

The ancient symbol is open to a wide variety of interpretations but is typically associated with a trinity of themes. For some, it represents life, death and rebirth;  past, present and future; and spirit, mind and body, just to name a few.

Still others associate the spirals with the Holy Trinity -- the Christian doctrine that describes God's makeup as the father, son and Holy Ghost.

One of the more common interpretations, which Google chose to focus, is that the spirals represent the three realms of the material world – earth, water and sky.

What ever your interpretation is, happy St. Patrick's Day!