Fatto generale: 1573 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 1573 is a value of n for which n, 2n, 3n, and 4n all use the same number of digits in Roman numerals.
Trivia: 1573 is an uninteresting number.
Data storica: 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".