And so I took my people from time to time in imitation of my idol Metaxas. I gave them a full day in early Byzantium, as Capistrano would have done, but I split it into six shunts. We ended our day’s work in 537, in the city Justinian had built on the charred ruin of the one destroyed by the rioting Blues and Greens.

“We’ve come to December 27,” I said. “Justinian will inaugurate the new Haghia Sophia today. You see how much larger the cathedral is than the ones that preceded it — a gigantic building, one of the wonders of the world. Justinian has poured the equivalent of hundreds of millions of dollars into it.”

“Is this the one they have in Istanbul now?” asked Mr. Real Estate’s son-in-law doubtfully.

“Basically, yes. Except that you don’t see any minarets here — the Moslems tacked those on, of course, after they turned the place into a mosque — and the gothic buttresses haven’t been built yet, either. Also the great dome here is not the one you’re familiar with. This one is slightly flatter and wider than the present one. It turned out that the architect’s calculations of thrust were wrong, and half the dome will collapse in 558 after weakening of the arches by earthquakes. You’ll see that tomorrow. Look, here comes Justinian.”

A little earlier that day I had shown them the harried Justinian of 532 attempting to cope with the Nika riots. The emperor who now appeared, riding in a chariot drawn by four immense black horses, looked a good deal more than five years older, far more plump and florid of face, but he also seemed vastly more sure of himself, a figure of total command. As well he should be, having surmounted the tremendous challenge to his power that the riots presented, and having rebuilt the city into something uniquely glorious.

Senators and dukes lined the approach; we remained respectfully to one side, amid the commoners. Priests, deacons, deaconesses, subdeacons, and cantors awaited the imperial procession, all in costly robes. Hymns in the ancient mode rose to heaven. The Patriarch Menos appeared at the colossal imperial door of the cathedral; Justinian dismounted; the patriarch and the emperor, hand in hand, entered the building, followed by the high officials of state.

“According to a tenth-century chronicle,” I said, “Justinian was overcome by emotion when he entered his new Haghia Sophia. Rushing to the apse, he gave thanks to God who had allowed him to achieve such a building, and cried out, ‘O Solomon, I have surpassed thee.’ The Time Service thought it might be interesting for visitors to this era to hear this famous line, and so some years back we planted an Ear just beside the altar.” I reached into my robes. “I’ve brought along a pickup speaker which will transmit Justinian’s words to us as he nears the apse. Listen.”

I switched on the speaker. At this moment, any number of other Couriers in the crowd were doing the same thing. A time will come when so many of us are clustered in this moment that Justinian’s voice, amplified by a thousand tiny speakers, will boom majestically across the whole city.

From the speaker in my palm came the sound of footsteps.

“The emperor is walking down the aisle,” I said.

The footsteps halted abruptly. Justinian’s words came to us — his first exclamation upon entering the architectural masterpiece of the ages.

Thick-voiced with rage, the emperor bellowed, “Look up there, you sodomitic simpleton! Find me the motherhumper who left that scaffold hanging in the dome! I want his balls in an alabaster vase before mass begins!” Then he sneezed in imperial wrath.

I said to my six tourists, “The development of time-travel has made it necessary for us to revise many of our most inspiring anecdotes in the light of new evidence.”

That night as my tired tourists slept, I slipped away from them to carry out some private research.

This was strictly against regulations. A Courier is supposed to remain with the clients at all times, in case an emergency occurs. The clients, after all, don’t know how to operate their timers, so only the Courier can help them make a quick escape from trouble.

Despite this I jumped six centuries down the line, while my tourists slept, and I visited the era of my prosperous ancestor Nicephorus Ducas.

Which took chutzpah, of course, considering that this was my first solo trip. But actually I wasn’t running any serious risks.

The safe way to carry out such side trips, as Metaxas had explained to me, is to set your timer carefully and make sure that your net absence from your tourists is one minute or less. I was departing from December 27, 537, at 2345 hours. I could go up or down the line from there and spend hours, days, weeks, or months elsewhere. When I had finished with my business, all I had to do was set my timer to bring me back to December 27, 537, at 2346 hours. From the point of view of my sleeping tourists I’d have been gone only sixty seconds.

Of course, it wouldn’t be proper to land at 2344 hours on the return trip, which is to say to come back a minute before I had left. There would then be two of me in the same room, which produces the Paradox of Duplication, a sub-species of the Cumulative Paradox, and is certain to bring a reprimand or worse if the Time Patrol hears of it. No: precise coordination is necessary.

Another problem is the difficulty of making an exact point-to-point shunt. The inn where my group was lodged in 537 would almost certainly no longer exist by 1175, the year of my immediate destination. I couldn’t blindly shunt forward from the room, because I might find myself materializing in some awkward place later constructed on the site — a dungeon, say.

The only safe way would be to go out in the street and shunt from there, both coming and going. This, though, requires you to be away from your tourists more than sixty seconds, just figuring the time necessary to go downstairs, find a safe and quiet place for your shunt, etc. And if a Time Patrolman comes along on a routine checkup and recognizes you in the street and asks you why the hell you aren’t with the clients, you’re in trouble.

Nevertheless I shunted down the line and got away with it.

I hadn’t been in 1175 before. It was probably the last really good year Byzantium had.

It seemed to me that an atmosphere of gathering trouble hung over Constantinople. Even the clouds looked ominous. The air had the tang of impending calamity.

Subjective garbage. Being able to move freely along the line distorts your perspective and colors your interpretation. I knew what lay ahead for these people; they didn’t. Byzantium in 1175 was cocky and optimistic; I was imagining all the omens.

Manuel I Comnenus was on the throne, a good man, coming to the end of a long, brilliant career. Disaster was closing in on him. The Comnenus emperors had spent the whole twelfth century recapturing Asia Minor from the Turks, who had grabbed it the century before. I knew that one year down the line, in 1176, Manuel was going to lose his entire Asian empire in a single day, at the battle of Myriocephalon. After that it would be downhill all the way for Byzantium. But Manuel didn’t know that yet. Nobody here did. Except me.

I headed up toward the Golden Horn. The upper end of town was the most important in this period; the center of things had shifted from the Haghia Sophia/Hippodrome/ Augusteum section to the Blachernae quarter, in the northernmost corner of the city at the angle where the city walls met. Here, for some reason, Emperor Alexius I had moved the court at the end of the eleventh century, abandoning the jumbled old Great Palace. Now his grandson Manuel reigned here in splendor, and the big feudal families had built new palaces nearby, all along the Golden Horn.

One of the finest of these marble edifices belonged to Nicephorus Ducas, my many-times-removed-great-grandfather.