To which Rosenthal adds: "They certainly thought their number was up. They had intimations. From their calendars, from the comets. They thought an age-cycle was coming to an end. Societies had come and gone - but as to whether another society was coming up - do we know? No, we don't. There was no major non-European military threat to the Aztecs at this time, in the way that the Aztecs had threatened other cultures when they came up. The Aztecs were a relatively recent invention, as it were."

We're back to that idea of the invented society. One which, however, anticipated its own demise. They did not know that their nemesis would be the Spanish, because they had no idea of another world across the water. They were not great sailors. They just knew there was going to be a big change. And when it came, they put up a hell of a fight, but perhaps, at the back of their minds, they knew it was pointless to resist. Perhaps they knew that they had to get through this final ritual conflict, and then disappear once more into legend.

Where did they come from? Where did they go to? It scarcely matters. The Aztecs are embedded in our consciousness. Their art is stunning. We will flock to see it, as the nation once flocked to the British Museum to see the treasures of Tutankhamun. Or so the Academy hopes. "I do think that the meeting of Europe with the last of the great ancient cultures was of cataclysmic historical importance," says Rosenthal. "It was like man going to the moon - except that on the moon, there was no follow-up."

With the Aztecs, there was as much follow-up as any civilization could wish. They may not have intended to quit while they were ahead, but that is exactly what they did. Montezuma's final revenge is that we are now more interested in his defeated, colourful society than we are in the brutal, incense-impregnated world of his conquerors.