Olivetti pointed to Piazza del Popolo and traced a straight line exactly southwest. The line missed, by a substantial margin, the cluster of black squares indicating Rome's major churches. Unfortunately, Rome's major churches were also Rome's older churches… those that would have been around in the 1600s.

She nodded. "No churches. From here the first one you hit is St. Peter's."

"They put the cardinal in the trunk."

Langdon looked over to the parked car where Olivetti and a group of soldiers now had a map spread out on the hood. "Are they looking southwest?"

Olivetti looked up. "Nothing. But this doesn't show every last church. Just the big ones. About fifty of them."

Langdon grunted. At least they were in agreement. He moved toward Olivetti. The soldiers parted to let him through.

Langdon swung off the scaffolding and dropped back to the ground. He brushed the plaster dust from his clothes. Vittoria was there to greet him.

"Where are we?" Langdon asked.

"No luck?" she said.

He shook his head.

"I've got some decisions to make," Olivetti said. "Are youcertain of the direction?"

"What's wrong with St. Peter's?" one of the soldiers said. He had a deep scar under his left eye. "It's a church."

Langdon pictured the angel's outstretched finger, the urgency rising in him again. "Yes, sir. Positive."

Langdon shook his head. "Needs to be a public place. Hardly seems public at the moment."

"Isn't there a monolith in the middle?"

Olivetti shrugged and traced the straight line again. The path intersected the Margherita Bridge, Via Cola di Riezo, and passed through Piazza del Risorgimento, hitting no churches at all until it dead-ended abruptly at the center of St. Peter's Square.

Langdon had already considered it. "No statues, though."

"But the line goes through St. Peter"sSquare," Vittoria added, looking over Langdon's shoulder. "The square is public."

She was right. There was an Egyptian monolith in St. Peter's Square. Langdon looked out at the monolith in the piazza in front of them. The lofty pyramid. An odd coincidence, he thought. He shook it off. "The Vatican's monolith is not by Bernini. It was brought in by Caligula. And it has nothing to do withAir." There was another problem as well. "Besides, the poem says the elements are spread acrossRome. St. Peter's Square is in Vatican City. Not Rome."

The guard shrugged. "The only reason I know about it is because I'm usually on piazza duty. I know every corner of St. Peter's Square."

Langdon was wide-eyed. "And you know of one in St. Peter's Square?"

"The sculpture," Langdon urged. "What does it look like?" Langdon was starting to wonder if the Illuminati could really have been gutsy enough to position their second marker right outside St. Peter's Church.

"Let's hear it," Olivetti pressed.

Langdon looked up. "What?"

"You're kidding," Langdon said. He had never known that.

"I patrol past it every day," the guard said. "It's in the center, directly where that line is pointing. That's what made me think of it. As I said, it's not really a sculpture. It's more of a… block."

"Always a bone of contention. Most maps show St. Peter's Square as part of Vatican City, but because it"soutside the walled city, Roman officials for centuries have claimed it as part of Rome."

"I only mention it," the guard continued, "because Commander Olivetti and Ms. Vetra were asking about a sculpture that had to do with Air."

"Not exactly. It's not really a sculpture. Probably not relevant."

"Depends who you ask," a guard interjected.

"Bassorelievo?"the guard asked, using the Italian art term.

"Relief,"Langdon said, "is the other half of sculpture!"Sculpture is the art of shaping figures in the round and also in relief. He had written the definition on chalkboards for years. Reliefs were essentially two-dimensional sculptures, like Abraham Lincoln's profile on the penny. Bernini's Chigi Chapel medallions were another perfect example.

Everyone looked at him.

Langdon stared at the young soldier in amazement. "A relief!" he exclaimed suddenly.

Olivetti looked mad. "A block?"

"Yes! Bas-relief!" Langdon rapped his knuckles on the hood. "I wasn't thinking in those terms! That tile you're talking about in St. Peter's Square is called theWest Ponente -- the West Wind. It's also known asRespiro di Dio."

"Yes, sir. A marble block embedded in the square. At the base of the monolith. But the block is not a rectangle. It's an ellipse. And the block is carved with the image of a billowing gust of wind." He paused."Air, I suppose, if you wanted to get scientific about it."

As the caravan of Alpha Romeos tore out of Piazza del Popolo, everyone was in too much of a hurry to notice the BBC van pulling out behind them.

"Breath of God?"

"Yes! Air! And it was carved and put there by the original architect!"

"Yes, thebasilica!" Langdon exclaimed, triumph in his voice. "But St. Peter"sSquare was designed by Bernini!"

Vittoria looked confused. "But I thought Michelangelo designed St. Peter's."