Fait mathématique: 1573 is a value of n for which n, 2n, 3n, and 4n all use the same number of digits in Roman numerals.
Culture générale: 1573 is an uninteresting number.
Date historique: April 21st is the day in 1863 that Bahá'u'lláh, the founder of the Bahá'í Faith, declares his mission as "He whom God shall make manifest".