At the end of my life – I am nearer the end than the beginning in these calm late-autumn days, I have been befriended by the marchesa's daughter, Maria Giovanna. She talks to me for hours as I sit in the garden at Cosimo's great house, doing my needlepoint. She remembers her mother and her sisters. Yesterday, she remembered the exciting days before the Council of Pisa.

In the sweet summer-like October of 1408, Rosa Dubramonte was twenty-two years old, the youngest of the four daughters of the Marchesa di Artegiana. She had a passionate nose, whose thrust was surrounded by a lascivious face of certain beauty, all supported by a professionally effulgent body. Maria Giovanna was the most womanly of the daughters; Maria Louise the most cunning; Helene the most vividly intellectual; but Rosa was the most intelligent. She thought her way through life's illusions and sensations and would trust in none of them, except at her mother's command, and unless she had good reason. Rosa had a mind which could herd mice at a crossroads, the Irish abbot MacMahon once said of her.

Rosa rode with an escort of six armed men from the establishment of her protector, Piero, Cardinal, Spina, through a countryside of vineyards and olive groves. Among the vineyards there were trees, including a great number of pomegranates which punctuated the distance with vivid colour. She rode under a broad scarlet straw hat, wearing slippers embroidered with pearls and a light, yellow riding cloak over a lime-green Chinese silk dress. She was travelling from Naples to a family conference in Perugia called by her mother. Her manufactured blondeness flashed in the wine-light of the lantern sun which hung at the eastern edge of the world. She would soon be with her family. They were almost across the valley, more than a thousand feet below the Etruscan walls of Perugia. Little of the town could be seen, but soon the climb towards its frescoes would begin, up the steep road that looped through the olive groves.

The marchesa's house in Perugia was set beyond the prior's palace, near the eastern wall of the city, standing at the end of a straight tree-lined drive whose entrance was flanked by stone figures of Juno and Venus. The main building was in two storeys, built partly in travertine, partly in Assisi limestone, with red and white marble from Bettona. It had a fine entrance doorway with a round arch, richly decorated by the Sienese artist Shanon Philippi, and in the lunette was a statue of St Ercolano, patron saint of Perugia, holding the hand of St Catherine of Pisa. There were lower recessed wings on either side of the central building; each end of these was flanked by curved buttresses. The whiteness of the architectural rhythm was emphasized by the stands of tall cypresses behind it.

Within the house, the piano noble was divided into rooms for the marchesa's daughters, arranged around a cruciform hall, each with a coved ceiling At the top of the cross, a square salon had been formed, from which a line of rooms extended to the left and right along the garden. The walls and ceilings of these rooms into the salon were decorated with frescoes by Giacomo Ricardo Blaca and painted at the zenith of his powers. The frescoes, masterpieces of trompe l'oeil, made each room appear to have been placed within open arcades overlooking the marchesa's native Pisan countryside on a perfect summer's day. Level valleys soothed beneath blue-tinged mountains, with vineyards, olive groves and chestnut trees, offering shade and peace.

At the base of the cruciform was the, main room. On the coved ceiling of the aula, Blaca had achieved a supreme triumph of illusionistic painting, in which an enormous figure of the marchesa, clothed in coloured silk, soared across the painted sky in a vastly calming composition, with the imagined heavens around her filled with a host of cherubims, flying or seated upon banks of clouds, all their small figures in the likenesses of the marchesa's daughters as babies.

On each side of the walls of the great rectangular room the Blaca frescoes depicted the same infants grown into the glowing, beauty of their childhood, all trooping away from the garden; entrance, but as they came nearer the main door they were each seen as having grown into youthful maturity, striding out to find the precious moments of their lives. It hadn't been like that in reality, but it gave them joy to see that that was how mama wanted it to be remembered.

The family assembled at noon in the main room, crowding around the marchesa, who had arrived last from Bologna. All of them were fashionably turned out in long, close-fitting laced or buttoned dresses with short-waisted bodices, wide low V- necks and wide belts under the arms and breasts. The border of the marchesa's skirt was gay with brocade. Each woman wore a small fashionable dagger at her girdle. They pulled chairs into a small circle so that the girls could face their mother.

`Frederick of Austria sends you special greetings, mama,' Maria Louise said. `I had no idea you were, up to something with him,'

`I can't tell you what it means to me to see all of you together,' the marchesa replied blandly.

'And how wonderful to have a few days; away from the insatiable Spina,' Rosa murmured.

'It isn't so much that Spina is insatiable,' the marchesa observed, 'but that.he is so determined to get his money's worth.'

`He wears a different disguise each time he does it!'

'Rosa! You know he needs to feel that perhaps you are not sure that, it is he in bed with you, so that he may deny it should you bring it up later. He is a cardinal, after all.'

'Really, you don't know, any of you. Spina is so devious that he will not allow a mirror in our bedroom, because if he saw himself reflected in one of those disguises he would have to accuse me of infidelity.'

The sisters all exploded with laughter.

`Sometimes I wish I had a lover like that,' Maria Giovanna said. 'My Cosimo is so careful that he won't make love in the daytime unless the shutters and blinds are closed and the curtains are drawn. Oh, don't misunderstand, please. He is merely very, very careful about everything.'

`He has a great deal to be careful about,' the marchesa said. `What is happening in Paris, Helene?'

'Never mind Paris. Paris will keep. Please, mama, why are we all here?'

The marchesa smiled a dangerous smile. `We are going to end the schism in the Church,' she said, `and elect Baldassare Cossa as the one true pope. And we are going to be richer and more influential than ever before.'

`Have you told Cosimo we will end the schism, mother?' Maria Giovanna asked.

`It was his father's idea and they will finance everything, so that, when it is done, the Medici bank will be the only bankers for the Church and they will be the richest bankers in the world. And this time we are going to have a real share in the action – a tithe of the bank's share and a tithe of Cossa's share as pope.'

Her audience was unable to speak or perhaps they were counting. Helene found her voice first. 'No woman has ever negotiated such a fee from her protectors,' she said with awe.

`Mama is the greatest courtesan who ever lived,' Rosa said proudly.

'Oh, mama!' Maria Giovanna cried. 'You are the idol of all womanhood,'

`Where do you begin with such a task?' Maria Louise asked. 'And how do we fit into it?'

`You are the keys to it,' the marchesa said. `As Cosimo has pointed out, Cossa controls the support of the canon lawyers, the theologians and the juridical faculty of the university. They are going to publish and justify – before the fact – the decision of the cardinals of both obediences to call a council of the Church.'

`Where will it happen?' Helene asked.

`Pisa. Everything is right for Pisa on this. It is close enough by sea from France yet it is in Italy, close to Florence, for the convenience of the Medici. Right now, Cossa is organizing the Bolognese jurists to lead an embassy to Florence to secure their agreement for a council at Pisa. Cosimo has everyone prepared in Florence. Helene will need to engage the University of Paris to persuade the king to intercede with all the princes of Europe to announce their neutrality towards the present popes.'