On 14 February 1564, a young Florentine living in Rome named Tiberio Calcagni heard rumours that Michelangelo Buonarroti was gravely ill. Immediately, he made his way to the great man’s home in the street of Macel de’ Corvi near Trajan’s Column and the church of Santa Maria di Loreto. When he got there he found the artist outside, wandering around in the rain. Calcagni remonstrated with him. “What do you want me to do?” Michelangelo answered. “I am ill and can find no rest anywhere.”

Somehow Calcagni persuaded him to go indoors but he was alarmed by what he saw. Later in the day, he wrote to Lionardo Buonarroti, Michelangelo’s nephew, in Florence. “The uncertainty of his speech togetherwith his look and the colour of his face makes me concerned for his life. The end may not come just now, but I fear it cannot be far away.” On that damp Monday, Michelangelo was three weeks short of his 89th birthday, a great age in any era and a remarkable one for the mid-16th century.

Later on, Michelangelo sent for other friends. He asked one of these, an artist known as Daniele da Volterra, to write a letter to Lionardo. Without quite saying that Michelangelo was dying, Daniele said it would be desirable for him to come to Rome as soon as he could. This letter was signed by Daniele and also underneath by Michelangelo himself: a weak, straggling signature, the last he ever wrote.

Despite his evident illness, Michelangelo’s enormous energy had still not entirely ebbed away. He remained conscious and in possession of his faculties, but was tormented by lack of sleep. In the late afternoon, an hour or two before sunset, he tried to go out riding, as was his habit when the weather was fine – Michelangelo loved horses – but his legs were weak, he was dizzy and the day was cold. He remained in a chair near the fire. All this was reported to Lionardo Buonarroti in a further letter sent that day. This was written in the evening by Diomede Leoni, a Sienese friend of the master, who advised Lionardo to come to Rome, but to take no risks in riding at speed over the bad roads at that time of year.

After another day in the chair, Michelangelo was forced to take to his bed. At his home were members of his inner circle: Diomede Leoni, Daniele da Volterra, his servant Antonio del Francese and a Roman nobleman, Tommaso de’ Cavalieri, some four decades his junior, who had been perhaps the love of Michelangelo’s life. Michelangelo wrote no formal will but made a terse statement of his last wishes: “I commit my soul into the hands of God, my body to the earth and my possessions to my nearest relatives, enjoining them when their hour comes to meditate on the sufferings of Jesus.” For a while, he followed the last of those recommendations himself, listening to his friends reading from the Gospels, passages concerning the Passion of Christ. He died on 18 February at about 4.45pm.

Thus ended the mortal existence of the most celebrated artist who had ever lived, indeed by many measures the most renowned to have existed until the present day. Few other human beings except the founders of religions have been more intensively studied and discussed. Michelangelo’s life, work and fame transformed for ever our idea of what an artist could be.

In 1506, when he was only 31 years old, the government of Florence described Michelangelo in a diplomatic communication with the Pope as “an excellent young man and in his profession unequalled in Italy, perhaps in the whole world”. At that point, he had almost six decades of his career still to come.

There was an epic quality to Michelangelo’s life. Like a hero of classical mythology, he was subject to constant trials and labours. Many of his works were vast and involved formidable technical difficulties: the huge frescoes of the Sistine Chapel ceiling and The Last Judgement, the marble giant David. Michelangelo’s larger projects – the tomb of Julius II, the façade and the new sacristy at San Lorenzo, the great Roman Basilica of St Peter – were so ambitious in their scale that he was unable to complete any of them as he had originally intended. However, even his unfinished buildings and sculptures were revered as masterpieces and exerted enormous influence on other artists.

Michelangelo continued to work, for decade after decade, near the dynamic centre of events: the vortex in which European history was changing. When he was born, in 1475, Leonardo da Vinci and Botticelli were starting out on their artistic careers. The Italian peninsula was a patchwork of small independent states, dukedoms, republics and self-governing cities. By the time he died, the Reformation and Counter-Reformation had taken place. The political and spiritual map of Europe had altered completely; France and Spain had invaded Italy and turned it into a traumatised war zone. The unity of Christendom had shattered: Protestants had split from the authority of the Pope in Rome. Catholicism was resurgent in a more tightly orthodox and militant form. A century of religious strife had begun.

While still in his mid-teens, Michelangelo became a member of the household of Lorenzo de’ Medici, the Magnificent, one of the figures around whom our idea of the Renaissance has coalesced. He worked in turn for no fewer than eight popes. He had grown up with the two Medici popes, Leo X (reigned 1513- 21) and Clement VII (reigned 1523-34), at the court of Lorenzo the Magnificent. The former spoke of him “almost with tears in his eyes” (but found him dauntingly difficult to deal with). With Clement VII, Michelangelo’s connection was even closer. According to Ascanio Condivi’s early biography, he regarded Michelangelo “as something sacred and he conversed with him, on both light and serious matters, with as much intimacy as he would have done with an equal”. Clement died in 1534 but Michelangelo still had 30 years to live and four more popes to serve.

The huge church of St Peter rose, very slowly, under his direction. Rome and Christianity metamorphosed around him. The Jesuit order and the Roman Inquisition were founded and Europe froze into a religious divide between Catholic and Protestant quite as ferocious and lethal as any of the ideological struggles of the 20th century. Still Michelangelo was there, acknowledged as the supreme artist in the world. Not just in his time, but of all time.

The day after Michelangelo died, an inventory was made of his goods. It listed the contents of a house that was sparsely furnished but rich in other ways. In the room where he slept there was an iron-framed bed with one straw mattress and three stuffed with wool, a couple of woollen covers and one of kid skin and a linen canopy. The clothes in his wardrobe suggested a touch of luxury, including a selection of black silken caps, two coats lined with fox fur and a fine cape. In addition, Michelangelo owned a variety of sheets, towels and underwear, including 19 used shirts and five new ones.

Apart from these, the house seemed bare. There was nothing in the dining room except some empty wine barrels and bottles. The cellar contained some big flagons of water and a half-bottle of vinegar. Two large unfinished statues – one of “St Peter”, perhaps in fact an effigy of Julius II once intended for his tomb; the other described as “Christ with another figure above, attached together” – remained in a workshop behind the house. There was also a little incomplete statuette of Christ carrying the cross.

Some drawings were found in Michelangelo’s bedroom, though a very small number in relation to the quantity he had made over the years. Most of these concerned his current building projects, particularly the Basilica of St Peter. Of the thousands of others he had made, some had been given away, some remained in Florence, where he had not set foot for almost 30 years, but a huge number had been deliberately destroyed by Michelangelo in a series of bonfires.

Also in the bedroom was a walnut chest. This was opened in the presence of the notaries carrying out the inventory. It turned out to contain, secreted in bags and small jugs of maiolica and copper, some 8,289 gold ducats and scudi, plus silver coins.

Michelangelo remarked: “However rich I may have been, I have always lived as a poor man.” Clearly, he was not joking, on either count. The inventory gives the impression of a decidedly spartan style of life; the gold and silver in that chest represented a fortune. Stored in his bedroom was a sum just a few hundred ducats short of the amount that Eleonora di Toledo, wife of Cosimo de’ Medici, the Duke of Tuscany, had paid 15 years before for one of the grandest dwellings in Florence: the Palazzo Pitti.

The gold in Michelangelo’s strongbox was considerably less than half of his total assets, most of which were invested in property. He was not only the most famous painter or sculptor in history, he was probably richer than any artist who had ever been. This was just one of many contradictions in Michelangelo’s nature: a wealthy man who lived frugally; a skinflint who could be extraordinarily, embarrassingly generous; a private, enigmatic individual who spent three-quarters of a century near the heart of power.

By the time Michelangelo died, the praise of him as “divine” was taken almost literally. Some, at least, regarded him as a new variety of saint. The strength of the veneration felt for him was similar to that in which martyrs were held. As a result, Michelangelo had two funerals and two burials in two different places.

The first was in Rome, in the church of Santi Apostoli not far from the house on Macel de’ Corvi, where the artist and pioneer art historian Giorgio Vasari described how he was “followed to the tomb by a great concourse of artists, friends and Florentines”. There Michelangelo was laid to rest “in the presence of all Rome”. Pope Pius IV expressed an intention of eventually erecting a monument to him in Michelangelo’s own masterwork, the Basilica of St Peter (at that point still a domeless building site).

This state of affairs was intolerable to Duke Cosimo de’ Medici, who for many years had tried without success to lure the old man to return to his native city. He resolved that Rome should not retain the artist’s corpse. The great man’s body was smuggled out of the city by some merchants, “concealed in a bale so that there should be no tumult to frustrate the duke’s plan”. Arrangements for an elaborate state funeral and interment were made. When the corpse arrived in Florence, on Saturday 11 March, it was taken to a crypt behind the altar in the church of San Pier Maggiore. There, the next day, the artists of the city assembled at nightfall around the bier, on which Michelangelo was now placed in a coffin covered by a velvet pall richly embroidered with gold. Each of the most senior carried a torch, which would have created a scene of sombre magnificence, the flickering flames illuminating the casket draped in black.

Next Michelangelo was carried in procession to the huge Gothic Basilica of Santa Croce, the heart of the quarter to which his family had always belonged. When word got around of whose body was being moved through the dark streets, a crowd began to assemble. Soon the procession was mobbed by Florentine citizens: “Only with the greatest difficulty was the corpse carried to the sacristy, there to be freed from its wrappings and laid to rest.” After the friars had said the Office of the Dead, the writer and courtier Vincenzo Borghini, representing the duke, ordered the coffin to be opened, partly – according to Vasari, who was there – to satisfy his own curiosity, partly to please the crush of people present. Then, it seems, something extraordinary was discovered.

Borghini “and all of us who were present were expecting to find that the body was already decomposed and spoilt”. After all, Michelangelo had been dead at this point for the best part of a month. Yet Vasari claimed: “On the contrary we found it [his corpse] still perfect in every part and so free from any evil odour that we were tempted to believe that he was merely sunk in a sweet and quiet sleep. Not only were his features exactly the same as when he was alive (although touched with the pallor of death) but his limbs were clean and intact and his face and cheeks felt as if he had died only a few hours before.”

Of course, an incorrupt corpse was one of the traditional signs of sanctity.

This is an extract from Martin Gayford’s “Michelangelo: His Epic Life” (Fig Tree, £30)