Istanbul's imperial heart

You begin at the bottom of the first hill, where the old city meets the Golden Horn. Sirkeci is a working corner of Istanbul rather than a showpiece: hans and small shops, boutique hotels, ferry horns from the piers a few streets over and the tram grinding past the station front. The Byzantines knew this shore as Prosphorion; today the same ground is a knot of suburban trains, trams and ferries, with the Marmaray line running underneath it. The walk climbs away from the water along Hüdavendigar Caddesi towards the dark line of the palace wall above the park. The station itself is the long stone hall with the big round window over its entrance, right behind the tram stop.

The high wall beside the tram tracks is the outer wall of Topkapi Palace, and you follow it for eight minutes, along Hüdavendigar Caddesi and then into the trees on Gülhane Parkı Sokağı. The park inside the wall was once the palace's outer garden, mostly grove. At its top end the Procession Kiosk sits on that wall above the tramway, the window from which sultans watched parades pass; across the road from it stands the gate of the Sublime Porte, the High Gate, which gave the whole Ottoman government its name. You are inside the park once the tram noise fades and tall plane trees close over the path.

Osman Hamdibey Yokuşu Sokağı carries you uphill for eleven minutes, the longest leg of the day. You are on the first of the old city's seven hills, the headland where Greek Byzantion had its acropolis and where the Ottomans later put their palace, and the rest of this walk never leaves it. The slope you climb carries the name of the painter who founded the museum at the top; yokuş simply means slope. Trees, cats and the hush of the old palace garden replace the traffic. You have arrived when the lane opens onto a courtyard where sarcophagi and column drums stand out on the grass under the trees, a long neoclassical front behind them.

From the museum gate the lane rejoins Osman Hamdibey Yokuşu Sokağı and the walkways carry you, in seven minutes, into the First Courtyard of Topkapi. This is the largest of the palace courts and the only one the city could enter, a walled park the Ottomans called the Court of the Janissaries, where officials and soldiers lined the path on days of procession. The plane trees here are enormous and the scale is deliberate; this was the sultans' front lawn. The court ends at the Gate of Salutation, a wall with two large pointed octagonal towers like a castle gatehouse, with an inscription dating it to at least 1542. Only the sultan was allowed to ride through it; everyone else, then as now, walks.

Five unhurried minutes back through the First Courtyard, which the Ottomans also called the Parade Court. Alongside the ceremonial path the court held the working buildings of the palace: among the trees stands the Imperial Mint, the Darphane-i Amire, built in 1727, where the empire's coins were struck within the sultan's own wall. Fountains sit at the edges, and stone, grass and gravel take over from the paving. Then, oddly for the courtyard of a sultan, a church: Hagia Irene is the plain red-brick building with a low dome and rows of arched windows, standing on its own among the trees close to the courtyard wall, and it looks older than everything around it.

Out through the Imperial Gate, the massive gateway the sultans rode in by, first built in 1478 and dressed in marble in the nineteenth century, and into the square outside, then along Soğukçeşme Sokağı. The square belongs to a fountain. Ahmed III built it in 1728, a square block under five small domes, a drinking fountain on each face and grilled windows at the corners where attendants handed out free water and sherbet; it was a gathering place for the whole city in the Tulip Period, and the oldest of its kind. It announces itself at once: a row of tall houses painted in pastels, bay windows stacked above the cobbles, pressed against the palace wall on one side.

Four minutes: down the length of Soğukçeşme Sokağı and onto Bab-I Hümayun Caddesi, the street named for the Imperial Gate behind you. Soğukçeşme Sokağı runs in the narrow gap between the palace wall and the back of Hagia Sophia, so for its whole length the great church's rear wall is the view. Tucked into this same tight corner, reached by a flight of steps from a side lane, is the Caferağa Medrese, a small college Sinan built in 1559 for Cafer Agha in Suleiman's reign; since 1989 its cells round the courtyard have held workshops where calligraphy, ceramics and jewellery are taught and sold. There is no mistaking the building you have come for: the rust-red mass of Hagia Sophia, buttress piled on buttress, a shallow dome between four minarets, fills the end of the street.

Round the front of Hagia Sophia and across Ayasofya Meydanı, five minutes. The square in front of the church is the open heart of the quarter, tour groups and simit carts and the two great buildings facing each other across the gardens. At its corner a battered stone pillar stands by itself: the Milion, the zero point from which the Eastern Roman Empire measured every road, a fragment re-erected after the houses above it were cleared and the ground excavated in 1967 and 1968. The cistern's entrance is a modest low building nearby, with nothing above ground to hint at what lies below; the lone pillar of the Milion is the sign you are in the right place.

The gardens between the two great buildings lead you through to the long open space beyond, six minutes. This is the Hippodrome, the chariot track of Byzantine Constantinople; the Ottomans called it At Meydanı, Horse Square, and the ancient track lies buried well below the present paving. At the top end stands the German Fountain, Kaiser Wilhelm II's thank-you for his 1898 visit to Sultan Abdülhamid II: made in Germany, shipped to Istanbul and assembled here, it was inaugurated on 27 January 1901, the Kaiser's birthday. That fountain is your marker: an octagonal domed pavilion on eight porphyry columns, gold mosaic glinting inside the dome, at the head of the square.

Along the long side of the square now, three minutes. The ground here is layered: the Byzantine emperors watched the races from the Kathisma, their box on this side of the track, joined by a passage to the Great Palace that spread down the hillside behind it towards the sea, and most of that palace now lies under the mosque and its Ottoman neighbours. As recently as 1993, an area in front of the mosque was bulldozed for a public building and turned up rows of Hippodrome seats and columns. The arrival is a cascade of grey domes and half-domes climbing to the main one, minarets at the corners, and the long arcaded courtyard wall in front of you.

Behind the mosque the ground is already tipping toward the Sea of Marmara, and Arasta Çarşısı Sokağı runs along the slope in a single straight line of small shops, three minutes from the courtyard wall. The whole hilltop leans this way: at the far end of the Hippodrome the Byzantines needed a curved wall of twenty-five vaulted arches to hold the track level on this same slope, and its lower arches still stand, the houses in front of them cleared only in the 1980s. Here the walk ends where it should, somewhere you can sit: a narrow lane of carpet and ceramic shopfronts under a low roofline, tea glasses on the tables outside, the grey domes of the mosque just above the roofs behind you, and the tram back at Sultanahmet a few minutes uphill.