A king for the Morea: the cipher of Pandolfo Malatesta's letter to Gianfrancesco Gonzaga, Rome, 22 April 1428 (Archivio di Stato di Mantova; DECODE R1854)

A Latin letter of Pandolfo Malatesta, archbishop of Patras, to his brother-in-law Gianfrancesco Gonzaga, lord of Mantua, written at Rome on 22 April 1428 (Archivio di Stato di Mantova, Archivio Gonzaga; image 1 of DECODE record R1854), hides its purpose in three passages of cipher, about 300 signs in all. Earlier attempts found no solution, and the letter was listed as unsolved by both public registers of historical ciphers in November 2026. Working from Satoshi Tomokiyo's transcription and checking every doubtful sign on the archive's image, this note gives the key and a complete reading. The cipher is a homophonic substitution of letter-like signs with two nulls; its Latin follows north-Italian spelling (x for s). The passages show Pandolfo, three days after the peace of Ferrara, urging Gonzaga not to disband his men-at-arms and proposing that he make himself, "without risk and without great expense", rex of the province of the Morea, for which he cites a Count Riciardo who had travelled there with their sister Cleofe Malatesta, the Despot Theodore II's basilissa.