like they've got a Biblion. Their index is computerized."
Vittoria looked hopeful. "That should speed things up."
Langdon wished he shared her enthusiasm, but he sensed this was bad news. He walked to a terminal and began typing. His fears were instantly confirmed. "The old-fashioned method would have been better."
"Why?"
He stepped back from the monitor. "Because real books don't have password protection. I don't suppose physicists are natural born hackers?"
Vittoria shook her head. "I can open oysters, that's about it."
Langdon took a deep breath and turned to face the eerie collection of diaphanous vaults. He walked to the nearest one and squinted into the dim interior. Inside the glass were amorphous shapes Langdon recognized as the usual bookshelves, parchment bins, and examination tables. He looked up at the indicator tabs glowing at the end of each stack. As in all libraries, the tabs indicated the contents of that row. He read the headings as he moved down the transparent barrier.
Pietro Il Erimito... Le Crociate... Urbano II... Levant...
"They're labeled," he said, still walking. "But it's not alpha-author." He wasn't surprised. Ancient archives were almost never cataloged alphabetically because so many of the authors were unknown. Titles didn't work either because many historical documents were untitled letters or parchment fragments. Most cataloging was done chronologically. Disconcertingly, however, this arrangement did not appear to be chronological.
Langdon felt precious time already slipping away. "Looks like the Vatican has its own system."
"What a surprise."
He examined the labels again. The documents spanned centuries, but all the keywords, he realized, were interrelated. "I think it's a thematic classification."
"Thematic?" Vittoria said, sounding like a disapproving scientist. "Sounds inefficient."
Actually... Langdon thought, considering it more closely. This may be the shrewdest cataloging I've ever seen. He had always urged his students to understand the overall tones and motifs of an artistic period rather than getting lost in the minutia of dates and specific works. The Vatican Archives, it seemed, were cataloged on a similar philosophy. Broad strokes...
"Everything in this vault," Langdon said, feeling more confident now, "centuries of material, has to do with the Crusades. That's this vault's theme." It was all here, he realized. Historical accounts, letters, artwork, socio-political data, modern analyses. All in one place... encouraging a deeper understanding of a topic. Brilliant.
Vittoria frowned. "But data can relate to multiple themes simultaneously."
"Which is why they cross-reference with proxy markers." Langdon pointed through the glass to the colorful plastic tabs inserted among the documents. "Those indicate secondary documents located elsewhere with their primary themes."
"Sure," she said, apparently letting it go. She put her hands on her hips and surveyed the enormous space. Then she looked at Langdon. "So, Professor, what's the name of this Galileo thing we're looking for?"
Langdon couldn't help but smile. He still couldn't fathom that he was standing in this room. It's in here, he thought. Somewhere in the dark, it's waiting.
"Follow me," Langdon said. He started briskly down the first aisle, examining the indicator tabs of each vault. "Remember how I told you about the Path of Illumination? How the Illuminati recruited new members using an elaborate test?"
"The treasure hunt," Vittoria said, following closely.
"The challenge the Illuminati had was that after they placed the markers, they needed some way to tell the scientific community the path existed."
"Logical," Vittoria said. "Otherwise nobody would know to look for it."
"Yes, and even if they knew the path existed, scientists would have no way of knowing where the path began. Rome is huge."
"Okay."
Langdon proceeded down the next aisle, scanning the tabs as he talked. "About fifteen years ago, some historians at the Sorbonne and I uncovered a series of Illuminati letters filled with references to the segno."
"The sign. The announcement about the path and where it began."
"Yes. And since then, plenty of Illuminati academics, myself included, have uncovered other references to the segno. It is accepted theory now that the clue exists and that Galileo mass distributed it to the scientific community without the Vatican ever knowing."
"How?"
"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