In J. R. R. Tolkien's legendarium, the history of the fictional universe of Eä began when the Ainur entered Arda, following the creation events in the Ainulindalë and long ages of labour throughout Eä, the universe. Time from that point was measured using Valian Years, though the subsequent history of Arda was divided into three time periods using different years, known as the , the and the . A separate, overlapping chronology divides the history into 'Ages of the Children of Ilúvatar'. The first such Age began with the Awakening of the Elves during the Years of the Trees and continued for the first six centuries of the Years of the Sun. All the subsequent Ages took place during the Years of the Sun. Most Middle-earth stories take place in the first three Ages of the Children of Ilúvatar.