The Celts had a great influence on Europe. It had left some of its traditions, history, art, religious customs, and even holidays which are still seen today.
Nowadays, when we hear about the Celts, Ireland and Scotland occurs to our mind. However, it is a name of a group of tribes which spread throughout Europe including Ireland and Britain who shared same religion, language and traditions.
Celtic nation existence was first recorded in the seventh century Before Christ by the Romans. The Roman Empire expanded throughout the center of Europe. Thus, the Celts thrived in Ireland and Great Britain where they have established.
The Celts had the Wheel of the Year calendar(pic.1), which is a symbol of the eight Sabbats (religious festivals). It included four solar festivals and four seasonal festivals (Winter Solstice, Spring Equinox, Summer Solstice, Autumn Equinox) it views the life circulation; birth, life, death, rebirth, almost as the seasonal changes.
Despite the impact and the rapid spread of Christianity in Europe, at some part Celtic culture have remained. For instance, many Celtic folklore stories, holidays and traditions are still seen in Ireland. Some of which went vital and in the present day are celebrated all around the world.
Resources:
1. https://pxhere.com/en/photo/40396
2. https://www.history.com/topics/ancient-history/celts