“We’re not sure, but most likely printed publications. He published many books and newsletters over the years.”
“That the Vatican no doubt saw. Sounds dangerous.”
“True. Nonetheless the segno was distributed.”
“But nobody has ever actually found it?”
“No. Oddly though, wherever allusions to the segno appear-Masonic diaries, ancient scientific journals, Illuminati letters-it is often referred to by a number.”
“666?”
Langdon smiled. “Actually it’s 503.”
“Meaning?”
“None of us could ever figure it out. I became fascinated with 503, trying everything to find meaning in the number-numerology, map references, latitudes.” Langdon reached the end of the aisle, turned the corner, and hurried to scan the next row of tabs as he spoke. “For many years the only clue seemed to be that 503 began with the number five . . . one of the sacred Illuminati digits.” He paused.
“Something tells me you recently figured it out, and that’s why we’re here.”
“Correct,” Langdon said, allowing himself a rare moment of pride in his work. “Are you familiar with a book by Galileo called Diаlogo?”
“Of course. Famous among scientists as the ultimate scientific sellout.”
Sellout wasn’t quite the word Langdon would have used, but he knew what Vittoria meant. In the early 1630s, Galileo had wanted to publish a book endorsing the Copernican heliocentric model of the solar system, but the Vatican would not permit the book’s release unless Galileo included equally persuasive evidence for the church’s geocentric model-a model Galileo knew to be dead wrong. Galileo had no choice but to acquiesce to the church’s demands and publish a book giving equal time to both the accurate and inaccurate models.
“As you probably know,” Langdon said, “despite Galileo’s compromise, Diаlogo was still seen as heretical, and the Vatican placed him under house arrest.”
“No good deed goes unpunished.”
Langdon smiled. “So true. And yet Galileo was persistent. While under house arrest, he secretly wrote a lesser-known manuscript that scholars often confuse with Diаlogo. That book is called Discorsi.”
Vittoria nodded. “I’ve heard of it. Discourses on the Tides.”
Langdon stopped short, amazed she had heard of the obscure publication about planetary motion and its effect on the tides.
“Hey,” she said, “you’re talking to an Italian marine physicist whose father worshiped Galileo.”
Langdon laughed. Discorsi however was not what they were looking for. Langdon explained that Discorsi had not been Galileo’s only work while under house arrest. Historians believed he had also written an obscure booklet called Diagramma.
“Diagramma della Veritа,” Langdon said. “Diagram of Truth.”
“Never heard of it.”
“I’m not surprised. Diagramma was Galileo’s most secretive work-supposedly some sort of treatise on scientific facts he held to be true but was not allowed to share. Like some of Galileo’s previous manuscripts, Diagramma was smuggled out of Rome by a friend and quietly published in Holland. The booklet became wildly popular in the European scientific underground. Then the Vatican caught wind of it and went on a book-burning campaign.”
Vittoria now looked intrigued. “And you think Diagramma contained the clue? The segno. The information about the Path of Illumination.”
“Diagramma is how Galileo got the word out. That I’m sure of.” Langdon entered the third row of vaults and continued surveying the indicator tabs. “Archivists have been looking for a copy of Diagramma for years. But between the Vatican burnings and the booklet’s low permanence rating, the booklet has disappeared off the face of the earth.”
“Permanence rating?”