Researchers are not sure how long Koreans have been celebrating Seollal. Many say that Seollal rituals date back to the 6th century. It was during the Three Kingdoms period of ancient Korea that the lunar calendar was first adopted. At that time, Seollal (also called Seol by some) was one of nine important festivals dedicated to ancestral ceremonies. Today, the remembrance of ancestors remains a common element of Korean New Year celebrations.