“What theory?”

“Having to do with the origin of the list of the Seven Wonders, of course.” He shook his head. “Ah, but look! There! Do you see it?”

Ahead of us and a bit to the left, a bright star appeared to be shining just above the horizon—even though the hour was noon.

“What can it be?” I whispered. I stared at the star that could not be a star, fascinated by the glimmering beam of light.

“Behold the Pharos!” said Antipater.

“Pharos?”

“It takes its name from the rocky island on which it stands, out in the harbor of Alexandria. Alexander founded the city, but it was his successor, King Ptolemy, who made the city great by constructing vast new temples and monuments. The greatest of these—certainly the most conspicuous—was a structure of a sort that had never been seen before, a soaring tower with a beacon at its summit to guide ships safely past the shallows and reefs to Ptolemy’s capital. A lighthouse, they called it. In the two hundred years since it was completed, similar towers have been built all over the world, wherever sailors are in need of a high beacon to guide them, but none of these later lighthouses are remotely as tall as the original, the Pharos of Alexandria.”

“But we must be a long way from Alexandria. I can’t see anything of the city at all.”

“The beacon can be seen across the open sea as far as three hundred stadia, they say—in Roman terms, thirty miles or more.”

“But how is such a light produced? Surely no flame can burn that brightly.”

“By day, the beam is created using mirrors—enormous reflectors made of hammered bronze and silver that can be tilted in various ways so as to reflect the light of the sun. At night, a bonfire is kept burning in the tower, and the mirrors magnify the light to make it many times brighter.”

“Remarkable!” I whispered, unable to take my eyes off the scintillating ray of light. Occasionally it appeared to flicker, distorted by waves of rising heat and the haze that hung over the tepid sea, but the light was strong and steady, growing brighter as our ship sailed closer to Alexandria.

At last I began to discern in miniature the features of a coastal city—ships in the harbor, city walls and towers, a vast temple on a hill in the distance—and most prominent of all, the lighthouse called the Pharos at the harbor entrance. At first my eyes deceived me, and I thought the Pharos was much shorter than it was. Then, as we drew nearer and the features of the city resolved themselves in greater depth, I was staggered at the true dimensions of the tower. I had thought it might be as tall as the Mausoleum in Halicarnassus, but it had to be much taller than that, at least twice or perhaps three times as tall.

“It must be as tall as the Great Pyramid!” I said.

I heard a chuckle behind me. “Not quite that tall—at least, not according to those who possess the knowledge and instruments capable of measuring such things.”

I tore my gaze from the Pharos to have a look at the smiling passenger who had just spoken, and who now joined us at the railing. His skin was the color of ebony and he had not a hair on his head, which made his white teeth and his necklace of silver and lapis all the more dazzling. I found it hard to judge his age, but he was not young; there were a few white hairs in his eyebrows. His flawless Greek had the elegant (to my ear, rather affected) accent of highly educated Alexandrians.

“My name is Isidorus,” he said. “Forgive me for intruding, but I couldn’t help but overhear your conversation. Have you truly seen all of the Seven Wonders of the World?”

“We have,” said Antipater.

“How remarkable! And I believe you mentioned the Library, and your desire to visit that institution.”

“I did,” said Antipater.

“I happen to be a scholar at the Library. Perhaps I can assist you in gaining access—unless, of course, you already have the necessary credentials.”

“As a matter of fact, any assistance you might give me would be most welcome,” said Antipater. “Allow me to introduce myself. I am Zoticus of Zeugma—no famous scholar, alas, merely a humble teacher of the young. And this is my pupil—or former pupil, I should say, for Gordianus is now a man and past the age of schooling.”

“A Roman?” said Isidorus.

I nodded. My accent always gave me away.

“You work at the Library?” said Antipater. “I thought the scholars there were seldom permitted to leave Alexandria, except on official business sanctioned by King Ptolemy.”

“That is correct. I’m just returning from a journey up the Nile. During the excavations for a new temple, some scrolls were discovered in a buried jar. They appeared to be very ancient. I was sent to retrieve them, so that they may be evaluated, copied, and catalogued in the Library.” Slung by a strap over one of his shoulders was a Roman-style capsa, a leather cylinder for carrying scrolls.

“Fascinating,” said Antipater. “May I ask what sort of documents these scrolls turned out to be?”

Isidorus laughed. “Don’t become too exited, friend Zoticus. The scrolls were in poor condition—the copiers will face quite a challenge, making sense of the faded script and the gaps. And from my cursory examination, they pertain mostly to day-to-day business among petty bureaucrats during the reign of some ancient pharaoh whom no one even remembers. Nothing to do with the Seven Wonders, I’m afraid.”

“Speaking of which…” I returned my gaze to the Pharos, which loomed even larger before us, so incredibly tall that it defied belief. “How can it be that this wonder is not listed among them?”

Isidorus smiled. “Certainly, we Alexandrians take great pride in the Pharos. But I can tell you, for a start, that it is not as tall as the Great Pyramid. Of course, the pyramids—and the Mausoleum, for that matter—are virtually solid constructions, made of stones stacked on stones with very little interior space. Given a large enough base, and enough stones, one could build such a construction to any height and it would remain stable—indeed, immovable, like a mountain. But such an edifice is by definition a monument, not a building of the sort that people can actually make use of, with hallways, rooms, stairwells, and windows. But the Pharos is such a building. There are hundreds of rooms inside, on many different levels—storerooms for fuel, workshops for the repair and upkeep constantly required by the complicated lighthouse mechanisms, dining halls for the workers, and barracks and armories for the soldiers who man the Pharos garrison. The Pharos does not merely exist to be gazed upon and marveled at. The Pharos is a working wonder.”

As we drew closer, I saw the soldiers and workers of whom Isidorus had spoken, moving purposefully across the island, up the long ramp that led to the lighthouse entrance, and manning the parapets of the tower. The soldiers wore exotic armor that mingled the traditions of Greece and Egypt. The workers wore a sort of uniform that consisted of a tight-fitting green cap and a dark green tunic.

I studied the details of the Pharos. The building was constructed of huge blocks of white stone, with decorations made of red granite; columns of this rose-colored stone framed the massive entrance. The tower rose in three distinct stages. The lowest and largest was square in shape; the four walls gently tapered inward as they rose and ended in an elaborately decorated parapet which featured gigantic Triton statues at each corner, each holding a trident in one hand and blowing a conch in the other. The middle portion was octagonal, and not as tall as the first. The final tower was cylindrical, and the shortest of the three. It was capped by the beacon, which appeared to be housed inside a colonnaded structure not unlike a round temple. Upon the roof of the Pharos stood a gilded statue, so distant that I was not sure which god it represented.