The guards at the Great Palace turned us away. None of them had ever heard of Justin, but they knew he was not of the gate contingent, for there had been no new appointments for more than a year. One of them suggested, however, that he might be part of the inner-palace scholae. "You could look for him there," the guard told me.

"If you will kindly tell me where to go, I will do as you advise," I replied, and was promptly told that it was impossible unless I had official business beyond the gate.

"But my business is with the Scholarae himself," I explained.

"No one is allowed into the inner-palace precinct without a formal summons," the gateman insisted. I thanked him for his help and resigned myself to leaving the city without seeing Justin again.

"Now we will go to The Church of Divine Wisdom," said Didimus, leading us back through the swarms of beggars who made their homes along the palace walls. "We will light a candle for your friend. We will perhaps light many candles."

Gunnar seemed well disposed to seeing the sights of the city one last time before sailing, and Tolar had seen nothing of Constantinople at all, so was happy to follow wherever we went. "I do not care where we go," Gunnar said, 'so long as I am there to collect my winnings from Hnefi."

"It is no distance at all," Didimus said. "I will return you to your ship in plenty of time, never fear. You are talking to the best guide in all Byzantium. Come with me, my friends, and I will show you the Hippodrome and the Forum of Augustus on the way."

The Hippodrome was impressive. The forum was a hollow square surrounded by two hundred columns, mostly taken from Greek temples, Didimus told us, because no one remembered how to make them like that anymore. I did not believe this, but the columns were definitely much older than the forum, so perhaps there was a small grain of truth in what he said. As imposing as these structures were, however, they shrank to insignificance beside the awesome achievement of the Hagia Sophia.

Heaven bless me, the Church of Holy Wisdom is a holy revelation made visible-a testament of faith in stone and mortar, a prayer in glass and tile and precious metals. The wonder of the world, it puts antiquity's much-vaunted architectural spectacles to shame. Sure, God himself inspired this church, and guided each and every labourer-those who put hand to trowel and beam, no less than he who conceived and drew the plans.

Just outside the forum, we four fell into step with the crowd entering the church, and passed directly into the first of two separate halls. Like many others, we paused before a chandler's stall for Didimus to purchase candles and incense, then walked quickly into the second, larger hall which was lined with huge slabs of red and green marble. The vaulted ceiling overhead was decorated with myriad stars and crosses picked out in gold. Above the towering bronze doors before us was a mosaic of the Virgin and Child; the divine infant held a small cross in his hand as if to bless all those who passed beneath his beneficent gaze.

Pushed along by the throng, we were swept under the mosaic, through the gate called Beautiful, and into the nave of the church. If from the outside Hagia Sophia's imposing red bulk appears heavy-a veritable mountain of brick and stone whose ponderous slopes rise above the surrounding trees, an enormous domed and mounded eminence girded about with massive masonry walls and giant supporting buttresses-on the inside, it is all light and air.

To step through the great bronze doors is to enter one of Heaven's own halls. Golden light streams from a thousand windholes, striking glints and gleams from every surface, falling from a dome as wide and open as the very sky. Miracle of miracles, there are no roof-trees of any kind at all under Sophia's dome-nothing obscures the glance or obstructs the eye as it soars up and up and up toward the exalted heights. The majestic dome hangs high above the marbled floor as if suspended from heaven by angelic hands.

The floor, as expansive as a plain, is all fine, polished marble; the double-tiered galleries high above the floor are marble also, deep-coloured and striking to the eye. There are screens and panels of marble, painstakingly carved with every manner of design: intricate geometrics, crosses, suns, moons, stars, birds, flowers, plants, animals, fish-everything, in fact, that exists in heaven and earth. The galleries are lined with enormous porphyry columns, the capitals of which have been carved into the shapes of plants; so cunningly have the sculptors practised their craft, it is as if the columns support masses of vines, luxuriant with leaves.

The galleries and corridors seemed endless; the high-pillared arches rose in tiers one above another. Above these were tall arched windholes, hundred upon hundred, admitting heaven's light. Though there must have been a thousand thousand people within the body of the church, such was its size that it could comfortably accommodate two or three times more again.

Almost every ceiling and pediment was covered with mosaics of the most elaborate design. The monks of the scriptorium are divinely adept at the intricacies of highly complex and sophisticated patterns; but even our good master at Kells could have learned much to his advantage from a close study of Sophia's panels and ceilings. Sure, the majesty of the church stole the breath from our mouths. Incapable of speech, Gunnar, Tolar, and I could but gape and stare, staggering from one marvel to the next, minds numb with wonder. And still we stared, drinking in each incredible sight as if it would be the last thing we would ever see.

Gunnar grew increasingly subdued, but not from boredom or lack of appreciation. Far from it! He gazed with amazement upon all he saw, and from time to time pointed out details of workmanship that I had missed. But his comments grew increasingly few and far between, and though he still appeared eager to capture every sight before him, his enjoyment took on the quality of rapture. Once, turning to see if he was still with me, I saw him standing before one of the gigantic carved screens, staring as if in a trance. He had his hand raised to the figure of a cross which had been carved into the panel as part of the design; and he was tracing the shape with his finger, repeating the motion again and again.

Gunnar seemed especially fascinated with the cross. Passing beneath the centre of the dome, I felt a touch at my shoulder and looked round to see the stout barbarian staring straight up at a golden mosaic of the largest cross I have ever seen. "His sign," Gunnar whispered, in a voice made small with awe. "It is everywhere."

"Yes," I answered, and explained that the cross was revered even as far away as Eire, the furthest limit of the empire. "Although the cross of the Byzantines is slightly different from the cross of the Celts, and that of the Romans is different again, yet they all honour the self-same sacrifice made by the Lord Christ for all men."

"So much gold," remarked Gunnar. Tolar nodded sagely.

Didimus led us to the left side of the nave where a free-standing panel had been erected to hold a number of large images painted on flat wooden boards. These icons bore the images of Christ, and various apostles and saints, which the people of Byzantium especially venerated. Before the panel, which Didimus called the iconostasis, rose a series of boards in stepped ranks which held the candles placed there by the worshippers. Taking his candles, Didimus lit one from those already burning, and placed it in one of the few empty holes in the plank. He stood for a moment rocking slightly back and forth, before taking a bit of the incense and sprinkling it over the flame. The incense struck the flame with a puff of fragrant smoke.