What is "illustrissimi"

Illustrissimi or "To the Illustrious Ones", is a collection of letters written by Pope John Paul I when he was Patriarch of Venice. The letters were originally published in the Italian Christian paper 'Messaggero di S. Antonio' between 1972 and 1975, and published in book form in 1976. The book was first published in English in 1978 when Cardinal Luciani (as he was then known) was elected Pope. As the English translation only reached the public after his death (after reigning as Pope for just 33 days), it stands as one of the few writings in public circulation that indicate what sort of person John Paul I was and what sort of Pope he might have been had he lived longer.