"the day when he attained enlightenment at Gaya in India; and the day he attained Nirvana (Unity with the Absolute) in 480 B.C." Because attaining enlightenmen

"the day when he attained enlightenment at Gaya in India; and the day he attained Nirvana (Unity with the Absolute) in 480 B.C." Because attaining enlightenment and nirvana are rational, factual, non-dogmatic "events" that can be dated.