Nine days in Provence: down the Rhone to the sea, from the popes' fortress to a Greek port

Walk up from the station into the Place du Palais and the whole of one side of it is the Palais des Papes. Seven popes ruled from here, and the building they left is the largest Gothic palace anywhere: twenty five rooms of scoured stone, because the Revolution used it as a barracks and a prison and stripped the decoration on the way through.

What survives repays the ticket. The pope's private study is painted floor to ceiling with hunting, fishing and orchards and has nothing religious in it at all, the great chapel could hold a village, and the roof terrace looks straight down at the river.

Then the Pont Saint-Bénezet, five minutes north. It was built in the 1180s and ran twenty two arches to the far bank, and the Rhône took them down so often that in the seventeenth century the town stopped rebuilding it. Four arches and a chapel now go out over the water and simply end. The song has everybody dancing on the bridge; they danced under it, on the island.

Twenty minutes south by train is a town that was one of the capitals of Roman Gaul and has never quite stopped living in the remains. The amphitheatre went up around AD 90 and held twenty thousand people; in the Middle Ages it was turned into a fortified village with two hundred houses and two chapels inside the ring, and it was not cleared out again until the nineteenth century. Three towers on top are what is left of that. It is still in use, for concerts and for the local bloodless bullfight, where a man tries to pull a rosette off the horns and generally ends up over the barrier.

Saint-Trophime is five minutes away on the main square. The twelfth century doorway is one of the great pieces of Romanesque carving in Europe, a Last Judgement across the whole front, and the cloister behind it changes from Romanesque to Gothic halfway round.

Walk out to the Alyscamps in the afternoon: an avenue of empty stone coffins under poplars, which was the burial road out of the Roman city and stayed in use for a thousand years. Van Gogh and Gauguin painted it side by side in the autumn of 1888, during the fifteen months he spent in this town producing about three hundred works and almost no sales.

The bus out takes about three quarters of an hour. The aqueduct is round the corner from the visitor centre and the size of it takes a moment to register: three tiers of arches, roughly fifty metres from the river to the channel on top, laid without mortar in blocks weighing several tonnes, carrying water fifty kilometres from a spring to the fountains of Roman Nîmes.

The museum by the car park is worth an hour before you walk out on it, because the interesting part is invisible: the canal drops only a few centimetres in every hundred metres over its whole length, surveyed and cut by men with wooden instruments and no way of seeing both ends. Swim off the shingle underneath if it is hot, and take the path up the far bank for the view.

Back in Avignon, spend what is left of the day in the Collection Lambert, which is two eighteenth century mansions full of contemporary art, and the last thing you would expect to find behind these walls.

Leave in the morning and be in Aix for lunch. The fast train takes twenty minutes to the TGV station out in the country and the shuttle bus another twenty into town; the coach from the middle of Avignon is slower and simpler.

Aix announces itself with water. The Fontaine de la Rotonde is a great circular basin of 1860 in the middle of the traffic, and behind it the Cours Mirabeau runs four hundred metres east under four rows of plane trees, laid out in the 1650s where the town wall used to be. The grand houses are on the shaded side and the cafés on the sunny one, and one of the fountains along the middle is fed by a thermal spring and steams on a cold morning.

Then get off it. Two streets north is Place d'Albertas, a small paved square of matched façades built in the 1740s by a family who wanted a decent view from their own door, with a fountain in the middle and musicians in it most evenings.

Book the studio for the morning. Cezanne was born in Aix in 1839, argued with the town for most of his life and built himself a workroom on the hill above it in 1902, with a north wall of glass and a slot in the side for moving large canvases. He worked there until he collapsed painting outdoors in 1906. The room has been left as it was: the coats, the skulls, the plaster cupid, the green jar and the ginger pot that turn up in still life after still life.

Walk back down to the Cathédrale Saint-Sauveur, which is three churches in a row rather than one: a sixth century baptistery with Roman columns under its dome, a Romanesque nave and a Gothic one beside it. The cloister is the reason to go in, small and wooden roofed with carved double columns, and usually empty.

Give the afternoon to the Musée Granet, which is far better than a town this size deserves. Provençal painting, the archaeology of Roman Aix, a group of Cezannes, and in a converted chapel a few hundred metres away on the same ticket, a private collection with Picasso, Klee, Braque and a Van Gogh in it.

Half an hour on the train or the coach and the whole register changes. Marseille is five times the size of Aix, three times as loud and considerably poorer, and the first thing to do with it is stand at the end of the Vieux Port, which is a rectangle of water with the city built up the hills on three sides and the fish sold off the boats on the quay every morning.

The Greeks landed here around 600 BC and put their town on the northern slope, which is now Le Panier: the oldest quarter, tight lanes going uphill, washing across the street, murals on every third wall, and a run of small shops selling soap and ceramics to visitors. It was dynamited in part by the Germans in 1943, so it is older in outline than in fabric.

Eat on the quay or above it, and take the evening slowly. The city has a rhythm that takes a day to pick up.

Everything on this day is on the strip of rock where the harbour meets the sea. Fort Saint-Jean was thrown up by Louis XIV in the 1660s with its guns pointing inland rather than out, which tells you what the king thought of Marseille, and the ramparts are now a public garden with two footbridges running off them.

One of those bridges crosses to the MuCEM, which opened in 2013 when the city was European Capital of Culture: a black concrete cube wrapped in a lattice cast to look like coral, with a ramp spiralling up the outside and a roof terrace over the sea. The museum inside is about the Mediterranean as a whole rather than about France, which is the right subject for this city.

Behind it stands the cathedral, La Major, an enormous nineteenth century pile in green and white striped stone, half Byzantine and half Romanesque and entirely out of scale with everything around it. Then walk back along the water for a drink where the ferries go out.

Notre-Dame de la Garde stands on the limestone hill south of the port with a gilded virgin on top of the bell tower, and the whole city can see it, which is the point. It is nineteenth century, striped like the cathedral, and the inside is hung with model ships, paintings of storms and thanks from sailors who got home. The terrace is the view of Marseille: the port, the islands, the hills, the sea.

Come down the north side to the Abbey of Saint-Victor, which is much older and much darker. There was a monastery here in the fifth century, built beside a Roman quarry that was already being used for burials, and the crypts underneath the present church hold sarcophagi and a chapel cut into the rock.

In the evening walk or take the bus out along the Corniche to the Vallon des Auffes, a fishing cove the size of a tennis court, wedged under a road bridge and lined with boats and three or four restaurants. This is where you order the bouillabaisse if you are going to: broth first with rouille and croutons, then the fish, filleted at the table, and a bill that will not surprise you if you have read the menu.

Start in Le Panier at the Vieille Charité, a seventeenth century almshouse designed by Pierre Puget with three storeys of arcades round a courtyard and an oval domed chapel in the middle of it. It was built to shut the poor away and it is now the most beautiful building in Marseille, holding an archaeology museum and a collection of African and Oceanic art.

Then Noailles, behind the top of the port, which is the market quarter and the part of the city that most obviously faces south rather than north: spice stalls, Tunisian pastries, fish, coriander by the armful, and prices from a different country. Buy soap, olive oil and whatever is in season.

The station is uphill from there, twenty minutes on foot or two stops on the métro, and the airport bus leaves from beside it.