work, like that of my colleagues, is based on the writings
of Aristotle," d'Aquino went on. "He has been called the Master of Those
Who Know. I call him _the_ philosopher. His thought encompassed every
subject under the sun--and the sun itself, I believe. The ancient
writers refer to a book by Aristotle called in Latin _De Caelestiis, Of
the Heavens_. In it _the_ philosopher writes about the movement of
heavenly bodies, the sun, the stars, and the planets, and their
relations with one another. That book disappeared during the long wars
that led to the downfall of the Roman Empire. Every time I meet a
traveler from some distant part of the world, I ask him about _De
Caelestiis_."

"Does it tell how the planets rule men's fates?" Daoud asked.

"That is a ridiculous, irrational, and superstitious notion." Fra
Tomasso waved the suggestion away with a stubby-fingered hand. Daoud
felt a cold wave of terror. Had he said something that gave him away?

But Fra Tomasso, leaning back in his squeaking chair, seemed
unperturbed. And Daoud remembered that Ugolini studied the influence of
the stars on human lives. So it could not be such an un-Christian
belief.

The Dominican pointed over his shoulder to the window of his cell, a
large rectangle cut in the curving whitewashed wall. This was one of the
few rooms Daoud had entered in Italy that was not covered with
idolatrous or obscene paintings, and he liked its austerity. Except, of
course, for the ubiquitous figure of Jesus the Messiah, crucified,
hanging opposite the window. Daoud tried to avoid looking at the
crucifixes because they reminded him of his childhood, but they were
everywhere in Orvieto.

"Aristotle reasoned about the relations of the heavenly bodies to one
another," Fra Tomasso said. "One account of the _De Caelestiis_ declares
that he believed that the sun does not move."

"But we see it move," Daoud said, surprised.

"We think we see it move." D'Aquino smiled. "But have you ever stood on
the deck of a galley as it was pulling away from the quay and had the
feeling that the quay was moving while the ship was standing still? Well
then, what if the earth is moving, just like a ship on whose deck we
stand, while the sun remains fixed?"

Daoud thought about the vast and solid earth and the daily journey of
the sun like a bright lamp across the sky. It was self-evident which one
of them moved. But he sensed that Fra Tomasso was in love with this
idea. He had be