In the center of the room, standing at a great table and leaning over a stack of documents, is a woman. She, too, is dressed in a simple white garment, and she also has very dark skin and eyes, and hair streaked with gray. The paper on the shelves and in the cubbies is stacked neatly and bound as books or rolled into scrolls and tied. The shelves are organized and labeled with stamped clay but he can’t read the letters. But he knows the lettering, thanks to his father, and he thinks, That is Greek.

The girl begins to talk to the woman, her voice pitched high, in a language Isaac doesn’t know. She pulls a codex book from her satchel and hands it to the woman, who places it on the table and braces her hands to read it. When she finishes and looks up again, her face is drawn.

Isaac thinks her beautiful even in age, with her thin face and lively eyes and curling hair pulled into a winding crown. But her expression makes his heart hurt.

She speaks to the girl, retrieves a stack of papers and sets it aside, then reaches into the depths of the shelf for something hidden at the back. From deep in the shadows she pulls out a large box, and after setting the box on the table she opens it and lifts out an object that she has to hold in two hands. An instrument made of brass.

It’s about the size of a dinner plate. Layers and parts all made of tooled brass, stacked together with gears and cogs. She turns the instrument and shows the girl what it does, explaining in rapid speech, and as she moves it, the plates twist and wind and the hands on a clockface rotate.

Isaac is reminded suddenly, sharply, of the great astronomical clock in the Old Town Square, with its complex gears and movements.

“Our clock in the square is an astrolabe, Isaac,” his grandfather had said. He was working on one of his own mechanical devices, standing over his messy kitchen table showing Isaac how he put his pieces together. “It not only tells the time but also the positions of the stars in the zodiac, of the sun and moon, and it’s a calendar, with months and years. And, imagine! It’s almost six hundred years old.”

And his grandfather added, “Long before that, the Greeks knew about astrolabes. The Antikythera mechanism that was found at the bottom of the Mediterranean Sea not so long ago is one such device.” He shook his head. “Such wonders in the ancient world.”

The Antikythera mechanism, Isaac thinks. The ancient world. This may be ancient Greece, then. That makes sense.

The woman is still explaining the workings of the mechanism to the girl. She’s talking fast, as if she’s in a great hurry.