Regarding the popes Gregory I (the one from the canticle) or Gregory XIII (the one from the calendar) and other characters of the same name.
A. In chronology. It was , calendar and year and we will announce reformed by Gregory XIII and followed today by almost all countries.
B. In the History of the Law School. Compilation of imperial constitutions made by a jurisconsult, of whom it is only known that his name was Gregory or Gregoriano, from whom he took the name de Codex Gregorian or Corpus Gregoriani. Although it was a work of character particular, carefully soon assumed great importance.