“This is the lounge for Couriers,” Capistrano said once more.

The Patrolman took no notice. When he finally left, five minutes later, I said, “Are they all like that?”

Protopopolos said, “This was one of the refined ones. Most of the others are boors.”

They put me to bed with a hypnosleep course in Byzantine Greek, and when I woke up I not only could order a meal, buy a tunic, and seduce a virgin in Byzantine argot, but I knew some phrases that could make the mosaics of Haghia Sophia peel from the walls in shame. I hadn’t known about those phrases when I was a graduate student at Harvard, Yale, and Princeton. Good stuff, hypnosleep.

I still wasn’t ready to go out solo as a Courier. Protopopolos, who was serving as staff router this month, arranged to team me with Capistrano for my first time out. If everything went smoothly, I’d be put on my own in a few weeks.

The Byzantium run, which is one of the most popular that the Time Service offers, is pretty standard stuff. Every tour is taken to see the coronation of an emperor, a chariot race in the Hippodrome, the dedication of Haghia Sophia, the sack of the city by the Fourth Crusade, and the Turkish conquest. A tour like that stays up the line for seven days. The fourteen-day tour covers all that plus the arrival of the First Crusade in Constantinople, the riots of 532, an imperial wedding, and a couple of lesser events. The Courier has his options about which coronations, emperors, or chariot races to go to; the idea is to avoid contributing to the Cumulative Paradox by cluttering any one event with too many tourists. Just about every major period between Justinian and the Turks gets visited, although we’re cautioned to avoid the years of bad earthquakes, and absolutely prohibited, under penalty of obliteration by the Time Patrol, from entering the bubonic plague years of 745-47.

On my last night in now-time I was so excited I couldn’t sleep. Partly I was keyed up over the fear of blundering somehow on my first assignment as a Courier; it’s a big responsibility to be a Courier, even with a colleague along, and I was afraid of committing some terrible mistake. The thought of having to be rescued by the Time Patrol upset me. What a humiliation!

But mainly I was worried about Constantinople. Would it live up to my dream of it? Or would it let me down? All my life I had cherished an image of that golden, glittering city of the past; now, on the verge of going up the line to it, I trembled.

I got up and stumbled around the little room they had given me, feeling drawn and tense. I was off all drugs and wasn’t allowed to smoke — Couriers have to taper off such things ahead of time, since it’s obviously an illegal anachronism to light up a weed in a tenth-century street. Capistrano had given me the dregs of his brandy, but that was small consolation. He heard me walking into furniture, though, and came to see what the trouble was.

“Restless?” he asked.

“Very.”

“I always am, before a jump. It never wears off.”

He talked me into going out with him to soothe our nerves. We crossed to the European side and wandered at random through the silent streets of the new city, up from Dolmabahce Palace at the shore to the old Hilton, and down past Taksim to the Galata Bridge and into Istanbul proper. We walked tirelessly. We seemed to be the only ones awake in the city. Through the winding maze of a market we wound, emerging on one of those streets leading to Haghia Sophia, where we stood a while in front of the majestic old building. I imprinted its features on my brain — the extraneous minarets, the late buttresses — and tried to make myself believe that in the morning I’d see it in its true form, serene mistress of the city, no longer compelled to share its grand plaza with the alien loveliness of the Blue Mosque across the way.

On and on we went, scrambling over the fragments of the Hippodrome, circling Topkapi, making our way to the sea and the old sea wall. Dawn found us outside the Yedikule fortress, in the shadow of the crumbling Byzantine rampart. We were half asleep. A Turkish boy of about fifteen approached us politely and asked, first in French and then in English, if we were in the market for anything — old coins, his sister, hashish, Israeli currency, gold jewelry, his brother, a carpet. We thanked him and said we weren’t. Undaunted, he summoned his sister, who may have been fourteen but looked four or five years older. “Virgin,” he said. “You like her? Nice figure, eh? What are you, American, English, German? Here, you look, eh?” She unsnapped her blouse at a harsh command from him, and displayed attractive taut round breasts. Dangling on a string between them was a heavy Byzantine bronze coin, possibly a follis. I peered close for a better look. The boy, breathing garlic at me, realized suddenly that it was the coin and not the breasts that I was studying, and made a smooth switch, saying, “You like old coins, eh? We find plenty under wall in a pot. You wait here, I show you, yes?” He ran off. The sister sullenly closed her blouse. Capistrano and I walked away. The girl followed us, calling out to us to stay, but by the time we had gone twenty meters she lost interest. We were back at the Time Service building in an hour, by pod.

After breakfast we got into costume: long silk tunics, Roman sandals, light cloaks. Capistrano solemnly handed me my timer. By now I had been well trained in its use. I slipped it in place against my skin and felt a dazzling surge of power, knowing that now I was free to transport myself to any era, and was accountable to no one so long as I kept in mind the preservation of the sanctity of now time. Capistrano winked at me.

“Up the line,” he said.

“Up the line,” I said.

We went downstairs to meet our eight tourists.

The jumping-off place for the Byzantium run is almost always the same: the plaza in front of Haghia Sophia. The ten of us, feeling faintly foolish in our robes, were taken there by bus, arriving about ten that morning. More conventional tourists, merely there to see Istanbul, flocked back and forth between the great cathedral and nearby Sultan Ahmed. Capistrano and I made sure that everybody’s timer was in place and that the rules of time-travel had been thoroughly nagged into everyone’s skull.

Our group included a pair of pretty young men from London, a couple of maidenly German schoolteachers, and two elderly American husband-and-wife outfits. Everybody had had the hypnocourse in Byzantine Greek, and for the next sixty days or so would be as fluent in that as in their native languages, but Capistrano and I had to keep reminding the Americans and one of the German girls to speak it.

We jumped.

I felt the momentary disorientation that always comes when you go up the line. Then I got my bearings and discovered that I had departed from Istanbul and had reached Constantinople.

Constantinople did not let me down.

The grime was gone. The minarets were gone. The mosques were gone. The Turks were gone.

The air was blue and sweet and clear. We stood in the great plaza, the Augusteum, in front of Haghia Sophia. To my right, where there should have been bleak gray office buildings, I saw open fields. Ahead of me, where the blue fantasy of Sultan Ahmed’s mosque should have been, I saw a rambling conglomeration of low marble palaces. To the side rose the flank of the Hippodrome. Figures in colorful robes, looking like fugitives from Byzantine mosaics, sauntered through the spacious square.

I swung around for my first view of Haghia Sophia without her minarets.

Haghia Sophia was not there.

On the familiar site I saw the charred and tumbled ruins of an unfamiliar rectangular basilica. The stone walls stood but precariously; the roof was gone. There soldiers drowsed in the shadow of its facade. I was lost.