IT WAS A HOT October afternoon in Rome, after most of the museums had closed for the day, when my friend Siu Li led me into the cool darkness of San Luigi dei Francesi, a 16th-century church just east of the Piazza Navona and west of the Pantheon. Siu Li was guiding me on a long-promised introduction to the city of her childhood, and there was something here she wanted me to see. At the rear of the church, in a chapel just left of the main altar, we gazed up at three astonishing masterpieces of early Baroque painting: a group of expansive canvases depicting scenes from the life of St. Matthew.

The effect these images had on me was surprising and immediate. On the left wall of the chapel was The Calling of St. Matthew, which shows the Apostle as a wealthy tax collector seated at a table with several men and boys, his bearded face illuimated by a single beam of light slanting down from the upper right corner of the canvas as shadowy figures of Jesus and St. Peter summon him to serve God. The image of Christ — his right hand hanging loosely before him in a gesture at once commanding and compassionate — captured my imagination in a strangely transfixing way, and I could feel quite distinctly Matthew's sense of fear and wonderment, his eyes wide open and the index finger of his right hand pointed incredulously at his own chest.

In the panel on the right, The Martyrdom, an angry and muscular warrior glares down at a frail, defeated Matthew lying helplessly at his feet amid a crowd of cringing onlookers. The explosive violence of the composition is tempered by an angel who leans delicately down from a puffy white cloud and reaches out to Matthew with a palm frond in a protective gesture that parallels the soldier's menacing sword. Like the Calling, this work is painted in dramatic chiaroscuro, with sharp contrast between light and dark emphasizing the pathos of the scene.

The central panel, a sweet, almost sensual depiction of St. Matthew and the Angel, shows the Apostle as a bright-eyed and balding old scholar dressed in orange and red robes, composing his Gospel with the help of an angel. Matthew leans awkwardly at a writing desk, resting his weight on a bench that seems to protrude from the canvas, and looks past his left shoulder toward the curly-haired angel hovering overhead. Their eyes meet in a moment of exceptional grace and unspoken communion, while the angel forms a gesture I found at once ambiguous and inexplicably poignant, the index finger of his left hand bent gracefully back between the thumb and index finger of his right hand.

All was quiet in San Luigi dei Francesi. The noise and pollution of central Rome dissolved into a vague and distant memory. The two of us stood there at length admiring the fine technique and compelling imagery of the three paintings, and I was overcome by a sense of joyful discovery, as if Siu Li had shared with me a miraculous vision or led the way to a rare and hidden treasure.

It was then I decided to embark on a pilgrimage through the galleries and churches of Rome in search of more works by the gifted young artist who in the summer of 1599 had been commissioned to decorate this chapel: Michelangelo Merisi da Caravaggio.

ROME, ENDLESSLY WONDERFUL and endlessly frustrating, does not introduce herself with a polite bow and a tidy presentation of her charms. Arriving there is like walking into a big, dusty and disorganized second-hand bookstore where lovely old leather-bound editions of Keats and Homer are tossed casually into bins with dime-store detective novels and well-thumbed paperback editions of bodice-ripping romances. For more than 2,000 years, the city has been a center of great art and architecture, and the remains of so many centuries of cultural wealth are scattered randomly about, sometimes literally in great heaps, much of it (though certainly not all) displayed with only the most rudimentary level of curatorship. There are ancient archaeological sites that lie unprotected and unexcavated, masterpieces of painting and sculpture crowded together in poorly lit galleries, brilliant Renaissance facades coated with black grime, venerable churches badly in need of restoration, and museums with little or no interpretive material to help you understand or even identify what you're looking at.

Rome holds many treasures, but just as the sheer quantity of artifacts has overwhelmed the public and private institutions charged with their stewardship, so too can the traveler be overwhelmed at every intersection by the daunting volume and variety of material to absorb. For this reason, the notion of choosing one artist to focus on was for me a welcome and reassuring way to lend structure to my explorations. No longer the aimless tourist, a haphazard consumer of aesthetic pleasures, I would become a secular pilgrim in Rome, immersing myself in the life and work of my own personal prophet, paying homage to his relics and devoting myself to his teachings.

Caravaggio was an ideal figure to venerate, for reasons both logistical and historical. On the practical side, the number of his works on public display in Rome (about 20, with some questionable attributions) is just enough to make the undertaking properly ambitious, but not so great that it could not be accomplished over the course of a few days. Moreover, the paintings are portioned out among a number of different museums and churches, so my search would lead me to various parts of the city and to some of Rome's most important collections, with ample opportunity to pursue other artistic tangents along the way.

Beyond these logistical considerations, I had chosen (or more precisely, been chosen by) a painter art historians rank among the most influential of his time, for Caravaggio was a leading figure in the early Baroque departure from the dominant tenets of 16th-century Mannerism. And to make matters even more interesting, Caravaggio's life — like the works he painted — was rife with drama and intrigue, as stormy and exciting as any swashbuckling adventure tale. (Indeed, this troubled and eccentric man has been the subject of two biographical novels: Caravaggio by Robert Payne and The Dark Fire by Linda Murray.)

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CARAVAGGIO WAS BORN in 1571 in the Lombardy region of northern Italy. Sometime around 1592, after a four-year apprenticeship with a painter in Milan, he traveled to Rome, which to an aspiring artist of the cinquecento was the equivalent of Hollywood to today's would-be film star. Living the bohemian life in Rome, he mingled with the urban poor and developed a painting style inspired by the harsh realities of his surroundings and by the unschooled faith of the lower classes. He received his first major public commission — the two side panels of the Contarelli Chapel at San Luigi dei Francesi — in 1599, and soon after was recognized as a celebrated artist, receiving numerous commissions over the next seven years for works both public and private.

But Caravaggio's fame was not without controversy, in part because he insisted on painting biblical figures directly from models of humble origin and questionable virtue, reproducing all the blemishes and imperfections of the human species — a practice that some art patrons and clergymen found highly distasteful. The controversy surrounding Caravaggio's painting style was exacerbated by persistent legal problems: It seems he suffered from an explosive temper that got him involved in more than a few violent brawls, and his name comes up frequently in court documents of the day. He was accused of armed assault on a number of occasions, of libel (by an artistic rival), of carrying a sword without a license, and once of throwing a plate of artichokes at a waiter. He was able to extricate himself from most of these charges, but in 1606 he was forced to flee from Rome after killing a certain Ranuccio Tommasoni following an argument over a tennis match.

During the next two years, Caravaggio continued to paint in exile, first in Naples and later in Malta, where he was received into the Order of the Knights Hospitaler of St. John. Then in October of 1608 his temper landed him in jail again, probably for quarreling with another knight; he managed to escape from prison, but was forced to flee in disgrace from the island. Stripped of his knighthood, he lived as a fugitive in Sicily for a year before returning to Naples in October 1609. In Naples he was attacked and seriously wounded by an unknown assailant, thought to be a disgruntled knight from Malta, and in the summer of 1610 he sailed from Naples to Port' Ercole on the coast of Tuscany, perhaps on his way back to Rome (the pope had issued an official pardon for the murder charge of 1606). Upon arrival in Port' Ercole, he was arrested once more, this time due to a case of mistaken identity. After two days in jail he was released, but his belongings were gone, still aboard the ship that had brought him from Naples and then sailed on. Overcome with fever and exhaustion, he died a few days later at the age of 39.

During his short career, Caravaggio had effected a significant change in the course of Italian art, popularizing an intensely theatrical style that brought biblical teachings to an earthy, emotional level and presented them as precise narrative moments appealing to the most basic levels of human experience. It was this quality of passion and accessibility that had drawn me so inexorably into Caravaggio's St. Matthew cycle, and I hoped to find more of the same compelling imagery as I pursued the goal I had set for myself that afternoon at San Luigi dei Francesi.

IN THE ENSUING DAYS, got up each morning and rode lumbering city buses into the center of town, where I marveled at the crumbling vestiges of ancient Rome and basked in the buzzing energy of modern Rome, walked the wide boulevards and followed momentary whims down intriguing dark alleys. But always between sightseeing stops and visits to gelaterias and pasticcerias I would dutifully find my way to the various museums and churches where I knew more Caravaggio works were on display. At each destination I would linger over the objects of my quest, examining every detail, losing myself in the powerful narrative impact of the paintings, letting their silent statements wash over me like the notes of a symphony. And although I tried to digest as much as possible the vast wealth of art and architecture surrounding me at every turn, it was Caravaggio who ultimately guided my steps through the streets where he lived and painted almost four centuries ago.

My explorations revealed a body of work at once vulgar and sublime, horrible and humorous. At the Galleria Borghese I saw a gruesome portrait of David holding up the severed head of Goliath, and at the Palazzo Barberini, an even more graphic and blood-spattered image of Judith slicing off the head of Holofernes with a frighteningly purposeful look of concentration.

At the Galleria Doria-Pamphilj was a tender portrait of a repentant Mary Magdalene with one glistening tear rolling down her nose, and next to it, a more complex and unusual composition, The Rest on the Flight into Egypt. In this work, a seated Mary tenderly cradles the baby Jesus on the right side of the canvas, and an angel, standing in graceful contrapposto at the center with his back to the viewer, plays the violin while a care-worn Joseph holds up a musical score. Close inspection reveals the artist's peculiar fascination with intricate and eccentric details: a bit of twisted string hanging from the pegs of the violin; the obtrusive black eye of a mule staring out from the bushes; the humbly crossed big toes of Joseph's bare feet. It is a melancholy scene, but also one of great peacefulness and purity, conveying at once the very human exhaustion of the journey and the divine strength that saw them through their exile.

At the Capitoline Museums I saw a gleefully (and quite frontally) nude St. John the Baptist shown as a small, carefree boy posing with a ram. Paintings such as this have fueled speculation that Caravaggio was gay, but the assertive sensuality of these images transcends, I think, the personal sexual preferences of the artist, who was equally capable of painting warmly sensual (though never nude) female figures.

At the Church of Sant' Agostino was a large painting of two pilgrims kneeling before a classically posed Madonna. The subject is taken from a legendary statue in Loreto said to have been brought to life by the prayers of the faithful, and the artist conveys with considerable success the delight and wonder seen in the faces of the poor and ragged pilgrims before this perfect vision of Mother and Child.

At the Church of Santa Maria del Popolo were two more large commissions, The Conversion of St. Paul, a contemplative look at a moment of divine ecstasy, and The Crucifixion of St. Peter, which focuses on the raising of the cross with Peter already attached in an inverted position. The Apostle accepts his fate grimly but without fear, apparently undaunted by the long spikes driven through his hands and feet, while three faceless laborers — like figures from a Thomas Hart Benton Mural — strain to lift his weight. In a perversely humorous gesture, Caravaggio filled the left foreground with one man's dirty feet and fleshy, protruding buttocks.

The paintings I was seeing encompassed a vast range of acts and emotions; they could be preciously beautiful or deeply disturbing, spiritually uplifting or profoundly melancholy. Some portrayed secular subjects, but most were based on biblical themes. Some were starkly representational, while others maintained elements of stylistic formality and symbolism typical of the Mannerists. But the one thing all of the works had in common was a fine touch of realism in the depiction of human figures and sentiments. These were not cold allegorical tableaux, but rich and captivating representations of familiar pains and pleasures, moments of tragedy and epiphany experienced by flesh-and-blood mortals bearing the names of saints. Each canvas added depth to my developing acquaintance with Caravaggio's rebellious spirit, and at the end of a week in Rome I had cultivated a strong sense of identity with the inventive, incisive mind that had conceived these extraordinary works of imagination.

THE FINAL STOP on my pilgrimage, one for which I had reserved a full day, took me to the Vatican Museums, where I spent the morning gazing up at the recently restored Sistine Chapel frescoes and then charging around among coagulations of tour groups through the unfathomable Christian and Pre-Christian collections held by the Roman Catholic Church. At midday, exhausted by the ordeal, I found my way to a sunny courtyard outside the museum restaurant and paused for an hour or so, drinking orange juice and writing letters, before venturing into the Pinacoteca Vaticana to see the last of the Caravaggios on my list: The Deposition of Christ.

Months later I read in the book Caravaggio by art historian John Gash that the Deposition was painted for a church associated with the Congregation of the Oratory, a populist sect founded by the 16th-century Christian mystic St. Filippo Neri. Neri rejected the elitist practices that had taken hold in the Catholic Church during the Renaissance and worked to involve lay people more fully in day-to-day spiritual practice. "It's interesting to speculate," Gash writes, "on Caravaggio's links with this highly influential religious movement which, with its emphasis on charitable works, congregational involvement, a minimum of ritual and a simple faith in keeping with the spirit of the Gospels, seems to have been as progressive a force in the popularization of religion as Caravaggio's own paintings." Gash's comparison of the visceral impact of Caravaggio's art with the populist appeal of Neri's back-to-basics theology was borne out by my own reaction to the Deposition.

This large canvas — 118 inches high and 80 inches wide — shows in vivid, lifelike detail the body of Christ being carried to his grave by two men, while the three Marys (the Virgin Mother, Mary Magdalene and the wife of Cleophas) grieve behind. Unlike other Caravaggio depictions of death, this one shows no graphic violence, no spurting blood, and the holes in the dead prophets hands and feet are mere dots on the canvas. More typical is the light which shines down from above and plays off every detail of Christ's almost naked body, revealing nuances of skin and muscle and vein that make his cold and lifeless flesh almost palpable against the shadowy background.

This is not a portrait of Christ in the spirit. Rather it shows him as a very human corpse, mouth open and eyes closed, his physical weight and substance emphasized by the clumsy postures of the men who bear him, by a rough grasping hand pulling at the wound in his side, and by one very small but striking detail: a lifeless finger snagged on the corner of a stone slab and bent forward by the weight of the same arm I had seen beckoning to Matthew in San Luigi dei Francesi. The composition includes not a hint of the impending resurrection of a prophet; it focuses instead on the death of a carpenter, and on the anguish of those who loved him.

As I studied the canvas, I began to share in their grief, moved to sadness by this 400-year-old view of personal loss and deep sorrow. But soon I found myself meditating on the tremendous influence this man has had on the history of human civilization, and so was drawn indirectly into a long, admiring contemplation of his spiritual legacy. My vaguely Quaker upbringing equipped me with only the most rudimentary biblical knowledge, but at that moment, Christ's basic messages of selflessness and love flooded my mind with a pervasive sense of truth and relevance, eclipsing my usual cynicism about the evils of over-institutionalized Christianity and leaving me with a renewed faith in the broad theological tradition into which I was born.

In retrospect, the irony is obvious: Succumbing to the stylistic flirtations of a long-dead painter, I had set out as a strictly secular pilgrim in search of graven images to worship; I ended up sitting teary-eyed and contemplative on a bench in the Vatican mourning the death of Christ and pondering the simple, persistent wisdom of his teachings. More ironic still is the fact that this miraculous transformation had been inspired not by a monk or a priest, nor even a philosopher, but by a violent and ill-mannered ruffian, a murderer even, whose singular imagination and skill with a paintbrush had spanned the centuries to touch this distant heart.