Am wondering if any of this is true (Hammett, The Maltese Falcon, p. 150).
"The archives of the Order from the twelfth century on are still at Malta. They are not intact, but what is there holds no less than three"—he held up three fingers—"referenees that can't be to anything else but this jeweled falcon. In J. Delaville Le Roulx's Les Archives de l'Ordre de Saint-Jean there is a reference to it—oblique to be sure, but a reference still. And the unpublished—because unfinished at the time of his death—supplement to Paoli's Dell' origine ed instituto del sacro militar ordine has a clear and unmistakable statement of the facts I am telling you."
"All right," Spade said.
"All right, sir. Grand Master Villiers de l'Isle d'Adam had this foothigh jeweled bird made by Turkish slaves in the castle of St. Angelo and sent it to Charles, who was in Spain. He sent it in a galley commanded by a French knight named Cormier or Corvere, a member of the Order." His voice dropped to a whisper again. "It never reached Spain." He smiled with compressed lips and asked: "You know of Barbarossa, Redbeard, Khair-ed-Din? No? A famous admiral of buccaneers sailing out of Algiers then. Well, sir, he took the Knights' galley and he took the bird. The bird went to Algiers. That's a fact. That's a fact that the French historian Pierre Dan put in one of his letters from Algiers.
Googling just turns up page after page about movie props.
Clarification: this question asks specifically the details about the falcon, starting with bare existance.
Addition: a book by Pierre Dan, unknown whether it contains the relevant letter.
It is not clear exactly how Hammett got his material. He is not known to have read French, medieval or otherwise, or Italian. His references must have been gleaned from a secondary source. I have been unable to locate a simple narrative of the rental agreement between the Hospitallers of St. John and Charles V of Spain that Hammett would have had available to him with all of the detail Gutman provides. I think there must be one; but what is clear, nonetheless, is that Hammett was reading widely, carefully and thoughtfully.