William deciphers the zodiacal code

On the afternoon of the third day, after the discovery of Venantius's corpse and the theft of a Greek book from his desk, William of Baskerville deciphered the cryptic message the dead translator had left behind. The page, found under Venantius's desk in the scriptorium, bore two layers of writing: a Greek text and, revealed by heat, a series of zodiacal signs. William, working in his cell with the parchment and his newly acquired lenses, cracked the code using a key derived from the order of the heavens and the zodiac, producing a Latin sentence that pointed toward the library's most forbidden zone.

The Method of Decipherment

William's approach combined his knowledge of Arabic cryptography, his familiarity with the library's catalogue, and a logical deduction about the order of signs. He recognized that Venantius had used a zodiacal alphabet, replacing letters with astrological symbols. The key, William reasoned, lay in the sequence of the heavens: Earth, Moon, Mercury, Venus, Sun, and the planets, followed by the twelve signs of the zodiac in their traditional order beginning with Aries. Applying this key to the necromantic signs Adso had copied, William transformed the jumble of symbols into a coherent Latin phrase: "Secretum finis Africae manus supra idolum age primum et septimum de quatuor." This translation, though grammatically awkward, was a breakthrough, revealing that the secret of the "finis Africae"—the library's most hidden chamber—could be accessed by manipulating the first and seventh letters of the word "quatuor" above an idol, which William later identified as the mirror in the south tower.

The Significance of the Discovery

William's decipherment was not merely a technical feat; it was the culmination of a chain of deductions that had begun with the first day's arrival at the abbey. He had already demonstrated his ability to read the "book of nature" by deducing the identity of the abbot's horse, Brunellus, from tracks in the snow. Now, he applied the same principle to a written text, treating the zodiacal signs as a system of signs that, once the correct code was found, yielded a specific meaning. The message itself was a riddle, but it confirmed that Venantius had discovered the key to the finis Africae and had recorded it before his death. This discovery transformed the investigation, shifting the focus from the series of murders to the forbidden book that lay at their heart, and it set the stage for William and Adso's eventual confrontation with Jorge of Burgos in the secret chamber.

The Limits of Knowledge

Despite his success, William remained acutely aware of the limitations of his method. The deciphered message was itself a puzzle, and he admitted to Adso that they still did not know what "the first and seventh of the four" meant or what the "idol" referred to. The code had been broken, but the deeper mystery—the nature of the book and the identity of the murderer—remained unsolved. This moment of triumph was thus tempered by a recognition of the incompleteness of human knowledge, a theme that would resonate through the novel's final revelations. William's pride in his intellectual achievement was genuine, but it was also a prelude to the greater humility he would later express when the library burned and the order he had sought to impose on events proved illusory.