"How much do you already know?" he asked. "I don't want to waste your time covering material you're familiar with."

"I know that the Mexica reached their imperial peak with the conquests of Ahuitzotl. He essentially proved the practical limits of Mesoamerican empire. The lands he conquered were so far away that Moctezuma II had to reconquer them, and they still didn't stay conquered."

"And you know why those were the limits?"

"Transportation," she said. "It was just too far, and too hard to supply an army. The greatest feat of Aztec arms was making the connection with Soconusco, far down the Pacific coast. And that only worked because they didn't take sacriftcial victims from Soconusco, they traded with them. It was more of an alliance than a conquest."

"Those were the limits in space," said Hunahpu. "What about the social and economic limits?"

She felt as if she were being given an examination. But he was right -- if he tested her knowledge first, he would know how deeply he could delve into the material that mattered, the new findings that he thought would answer the great question of why the Interveners had given Columbus the mission of sailing west. "Economically, the Mexica cult of sacrifice was counterproductive. As long as they kept conquering new lands, they took enough captives from warfare that the nearby territory could maintain enough of a workforce to provide food. But as soon as they began coming back from war with twenty or thirty captives instead of two or three thousand, they were left with a dilemma. If they took their sacrifices from the surrounding lands they already controlled, food production would go down. But if they left those men on the land, then they would have to cut down on their sacrifices, which would mean even less power in battle, even less favor from, the state god -- what was his name?"

"Huitzilopochtli," said Hunahpu.

"Well, they chose to increase the sacrifices. As a sort of proof of their faith. So production fell and there was hunger. And the people they ruled over were more and more upset at the taking of sacrifices, even though they were all believers in the sacrificial religion, because in the old days, before the Mexica with their cult of Witsil ... Huitzil --"

"Huitzilopochtli."

"There'd be only a few sacrifices at a time, comparatively speaking. After ceremonial war, or even after star war. And after the ball games. The Mexica were new, with their profligate sacrificing. The people hated it. Their families were being torn apart, and because so many people were sacrificed it didn't seem to be such a sacred honor anymore."

"And within the Mexica culture?"

"The state thrived because it provided social mobility. If you distinguished yourself in war, you rose. The merchant classes could buy their way into the nobility. You could rise. But that ended immediately after Ahuitzotl, when Moctezuma virtually ended all possibility of buying your way from class to class, and when failure in war after war meant that there was little chance of rising through valor in battle. Moctezuma was in a holding pattern, and that was disastrous, since the entire Mexica social and economic structure depended on expansion and social mobility."

Hunahpu nodded.

"So," said Diko, "where do you disagree with any of this?"

"I don't disagree with it at all," he said.

"But the conclusion that is drawn from this is that even without Cortes, the Aztec empire would have collapsed within years."

"Within months, actually," said Hunahpu. " Cortes's most valuable Indie allies were the people of Tlaxcala. They were the ones who had already broken the back of the Mexica military machine. Ahuitzotl and Moctezuma threw army after army against them, and they always held on to their territory. It was a humiliation to the Mexica, because Tlaxcala was just to the east of Tenochtitlan, completely surrounded by the Mexica empire. And all the other people, both those who were still resisting the Mexica and those who were being ground to dust under their government, began to look to Tlaxcala as their hope of deliverance."

"Yes, I read your paper on this."

"It's like the Persian Empire after the Chaldean," said Hunahpu. "When the Mexica fell, it wouldn't have meant a collapse of the entire imperial structure. The Tlaxcalans would have moved in and taken over."

"That's one possible outcome," said Diko.

"No," said Hunahpu. "It's the only possible outcome. It was already under way."

"Now we come to the question of evidence, I'm afraid," said Diko.

He nodded. "Watch."

He turned to the TruSite II and began calling up short scenes. He had obviously prepared carefully, for he took her from scene to scene almost as smoothly as in a movie. "Here is Chocla, " he said, and then showed her brief clips of the man meeting with the Tlaxcalan king and then meeting with other men in other contexts; then he named another Tlaxcalan ambassador and showed what he was doing.

The picture quickly emerged. The Tlaxcalans were well aware of the restiveness both of the subject peoples and of the merchant and warrior classes within the Mexica homeland. The Mexica were ripe for both a coup and a revolution, and whichever one happened first would certainly trigger the other. The Tlaxcalans were meeting with leaders of every group, forging alliances, preparing. "The Tlaxcalans were ready. If Cortes had not come along and thrown a monkey wrench into their plans, they would have slipped in and taken over the entire Mexica empire, whole. They were setting it up to have every subject nation that mattered revolt all at once and throw their might behind Tlaxcala, trusting in the Tlaxcalans because of their enormous prestige. At the same time, they were going to have a coup topple Moctezuma, which would break up the triple alliance as Texcozo and Tacuba abandoned Tenochtitlan and joined in a new ruling alliance with Tlaxcala."

"Yes," said Diko. "I think that's clear. I think you're right. That's what they planned."

"And it would have worked," said Hunahpu. "So all this talk about the Aztec Empire being ready to fall is meaningless. It would have been replaced by a newer, stronger, more vigorous empire. And, I might point out, one that was just as viciously committed to wholesale human sacrifice as the Mexica. The only difference between them was the name of the god -- instead of Huitzilopochtli, the Tlaxcalans committed their butchery in the name of Camaxtli."

"This is all very convincing," said Diko. "But what difference does it make? The same limits that applied to the Mexica would apply to the Tlaxcala people as well. The limits on transportation. The impossibility of maintaining a program of wholesale slaughter and intensive agriculture at the same time."

"The Tlaxcala were not the Mexica," said Hunahpu.

"Meaning?"

"In their desperate struggle for survival against a relentless, powerful enemy -- a struggle which the Mexica had never faced, I might add -- the Tlaxcala abandoned the fatalistic view of history that had crippled the Mexica and the Toltecs and the Mayas before them. They were looking for change, and it was there to be had."

By now, it was getting late in the workday, and others were gathering around to watch Hunahpu's presentation. Diko saw now that the fear had left Hunahpu, and so he was becoming passionate and animated. She wondered if this was how the myth of the stoic Indie had began -- the cultural response to fear among the indie looked like impassiveness to Europeans.

Hunahpu began to take her through another round of brief scenes showing messengers from the king of Tlaxcala, but now they were not going to Mexica dissidents or subject nations. "It is well known that the Tarascan people to the west and north of Tenochtitlan had recently developed true bronze and were experimenting heavily with other metals and alloys," said Hunahpu. "What no one seems to have noticed is that the Mexica were completely unaware of this, but Tlaxcala was right on top of it. And they aren't just trying to buy the bronze. They're trying to co-opt it. They're negotiating for an alliance and they're trying to bring Tarascan smiths to Tlaxcala. They will certainly succeed, and that means that they'll have devastating and terrifying weapons unavailable to any other nations in the area."