The "Lettera Rarissima" is Columbus' Report and published text of his letter describing His Last Voyage of Discovery to The New World in the year 1502-3.
Only one printed contemporary copy (in the Marciana Library in Venice)and one handwritten contemporary copy (in the Karpeles Manuscript Library)survive.
In this letter, Columbus describes, for the first time, the mainland coasts of the his prior 3 visits reached only outlying islands. He concludes with confidence that he has, at last, reached the Indies China is clearly the next kingdom down the coast.
Contrary to bright and cheery descriptions of the lush landscapes and the abundant fruit as described in "The Columbus Letter", the "Lettera Rarissima" tells of difficulties, disasters and storms....reflecting the disappointment of Columbus in not getting proper recognition and rewards for his momentous discoveries.
The name "Lettera Rarissima" is used in history books to describe the amazing story of it's transmittal.
In particular, in1503, Columbus was stuck in Jamaica, and his ship was dangerously broken. He could not move forward. He could not stay either on this island because of the fear of savage's attack. So he stayed in his ship, with 120 other men. His only hope was to send a messenger (carrying this letter) to ask for rescue. They were 70 miles away from the port of Santo Domingo, and the sea, the storm, the current made this mission a total suicide. Columbus rescue was in the hands of god.
The 7th of July, he wrote this letter. At his demand, 18 volunteers decided to risk their lives in a small boat with oars, in order to bring this rescue letter to Santo Domingo, and then to the Kings of Spain.
The story of the mission of those 18 volunteers is amazing. They defied storm, enormous weaves, have been captured by Indians pirates, escaped, have been lost in the sea ... then finally Diego Mendez saw the main island and after a night of rowing they finally arrived. He decided to walk alone 50 more miles in the jungle to find the governor Ovando, to finally give him this letter.
Columbus was rescued after spending 9 month on his broken ship. This rescue is truly a miracle and his letter has endured so many dangers before to arrive at destination, that a librarian in Venice decided to call it "Lettera Rarissima".

The Karpeles Manuscript Library thanks M. Yann Robert of Paris France for the information on the naming of this letter.