Borromini: the first architect

'Once Borromini has bitten you he never lets go." So, in 1948, Anthony Blunt, surveyor of the king's pictures, advised Kerry Downes, a budding architectural historian who had recently gone up from Ealing Priory School to the Courtauld where Blunt was director. Downes had written Blunt a "dreadful, if enthusiastic" first essay on the work of Francesco Borromini, the 17th-century baroque architect. Although notoriously aloof, Blunt had spotted a spirited fellow enthusiast for the most exhilarating, if controversial, of all Roman architects – indeed of all architects of all eras – and Borromini had certainly got his teeth into Downes.

The young man would become a distinguished architectural and art historian, who would write books on Hawksmoor, Vanbrugh and Wren. And now, all these years later, he has published his first on Borromini. Borromini's Book, with its suitably baroque subtitle, "The 'Full Relation of the Building' of the Roman Oratory by Francesco Borromini and Virgilio Spada of the Oratory" – is a magisterial work representing six decades of meticulous scholarship and a serpentine tale that refuses to end 350 years after the architect of the Roman Oratory committed suicide by running himself through with a sword. He was ill, and it was, says Downes, "a theatrical cry for help".

But then the Baroque was a highly dramatic style. A wayward child of the high renaissance, it was broken in by Michelangelo in the 16th century and given full rein by Bernini and Borromini in the 17th. Baroque buildings were characterised by curves, domes, broken pediments and a gloriously inventive play on classical detailing. At its height, it was a kind of full-blooded and thrilling architectural opera, a world very much apart from the chaste and graceful design that ousted it the 18th century. Deeply romantic, it also had something of the subversive about it.

When Downes wrote that first fumbling essay, Borromini was still widely considered to be eccentric, and possibly even psychotic. His swirling buildings appeared to dance wildly before uncomprehending eyes. Even today, his Roman churches of Sant'Ivo alla Sapienza and San Carlo alle Quattro Fontane are as sensational as they are beautifully realised, while the laziest guidebooks still disparage his demanding talent. His façade for the Palazzo di Propaganda Fide in Rome remains disturbing, even a little frightening, while his complex and enigmatic Oratory for the congregation of Catholic priests founded by St Philip Neri in the 1550s is one of the world's least obviously great buildings.

Its inwardly curving façade was unusual; so, too, was the fact that the glorious rooms that run through it follow a plan that is more an adventure than anything rational; here is the birth of what one might call narrative architecture, with sudden and unexpected twists and turns in its stirring plots. It is a building you have to walk through slowly, eyes wide open.

In an age when a new baroque appears to have swirled into life through the voluptuous designs of Frank Gehry and Zaha Hadid, Borromini and his restlessly alive architecture are as provocative as ever. Working with a single assistant and with pen and paper, the 17th-century architect produced buildings of an artistic and structural complexity that would challenge the most imaginative architect armed with a spaceship's worth of computers and hi-tech materials.

Because the Oratory and Borromini's life, works, influence and critical reputation, are so complex, Downes has produced a very different book from conventional art historical monographs. The first of its two distinct halves is an engaging translation of "Borromini's Book". Here is Borromini telling his own story and describing his working methods through the design and building of the Oratory to his friend and client, Monsignor Virgilio Spada. The "Full Relation" was published only in 1725, long after Borromini's death. Downes's translation is printed on the righthand pages with the English author's commentary on the left.

The second half of the book is Downes on Borromini. Seven thorough, yet readable sections, explain the church and papacy of the time, and the nature of the Oratorians – a society of priests founded by St Philip Neri – as well as Borromini's life, ideas, works, rivalries, dramas and death, and his posthumous reputation.

Not only has Downes produced a magnificent play on Borromini and his challenging buildings but he has exposed a baroque solar system, with characters spinning like planets around their star – Borromini – down through the centuries since his death; spinning, not in polite circles, but in elaborate geometries.

Born Francesco Castelli in 1599, the star was a tall and handsome stonemason. As a teenager he travelled from his home town of Bissone, in what is now the Swiss canton of Ticino, to Milan, where he worked on the city's slow-born Gothic cathedral. From there he went to St Peter's in Rome, recently crowned with Michelangelo's awe-inspiring dome. When he set up on his own as an architect in 1633, he changed his name to Borromini – a play, perhaps, on both St Charles Borromeo, whose name graced his first solo commission, the breathtaking Roman church of San Carlo alle Quattro Fontane, and on his rival Bernini, the "Uomo Universale".

Borromini was one of the first truly professional architects. Architecture was a matter of life and death to him; while working on his sumptuous rebuilding of the great early Christian basilica, San Giovanni in Laterano, he surprised a man, according to Downes, "in flagrante damaging some ornament and, in particular, smashing up, spitting on and disfiguring some slabs of stone". Borromini had the man beaten up, and when the man died, was granted a papal pardon.

Driven, studious, solitary, dressed in austere Spanish fashion, unmarried and probably chaste, Borromini set up home with an assistant and housekeeper in sparsely furnished rooms near San Giovanni dei Fiorentini. There was a bust of his hero, Michelangelo, a plaster cast of the Stoic philosopher, Seneca, and a library of around 1,000 books. It was here that he dreamed up his complex designs in the knowledge that "in inventing new things one cannot receive the fruit of one's labour except later". Here he shaped the revolutionary façade of the Oratory – "I imagined a human form with open arms as if embracing everyone entering," – and quietly railed against what he thought of as the parsimony of the Oratorians – "I have had to serve a congregation of souls so humble that they have held back my hand in adornment." It was here that he brooded on his rivalry with Bernini, a gregarious womaniser who, when he did marry, lived in a palace fit for a pope; and here that, for whatever reason, Borromini killed himself.

Where Bernini was suave, Borromini was grave; where Borromini worried, Bernini celebrated. Bernini used Borromini when it suited him, and very probably exploited him through a number of papal commissions, including the St Peter's baldacchino, the mighty, barley-sugar-columned canopy that sits theatrically under Michelangelo's dome. This tore at Borromini's soul.

Borromini's was surely a life lived baroquely, and his reputation was dealt with in no less a manner. Bernini needled him, but after his death, he told Spada that "only Borromini understood this profession, but that he was never content and that he wanted to hollow out one thing inside another, and another inside that without ever getting to the end." In Paris in 1665, working on the Louvre, Bernini told Paul Freart de Chantelou, the wealthy art collector, "a painter or a sculptor in their architecture take as their guides to proportion the human body, but Borromini must have based his on chimeras."

It was not until the 1920s that German art historians began to reassess Borromini, and only in the 1940s that his genius was revived and restored. In Britain, the baroque had been associated with papal conspiracies and over-elaborate decoration. Even Wren had been written off by the Palladians. Borromini was far beyond the pale. Until recently, there have been historians who have denied the very existence of an English baroque; English Baroque Architecture (1966) was the title of Kerry Downes's first important book. The baroque, though, began to appeal, at first surreptitiously, not just to those who looked to Rome – as Evelyn Waugh had – but also to those such as Blunt whose ostensibly uptight, upright manner fronted hidden passions – among them his sexuality – and who sought subversion (Blunt was a Soviet spy.) "We appreciate a struggle between opposites," he wrote in his succinct 1979 study of Borromini, "not as the romantics did, in the expectation of defeat, but in the hope that a synthesis will be achieved." He might have been writing about himself.

So, the baroque became a cloak-and-dagger saga – a story lived out behind crimson Roman Catholic and blood-red Communist curtains, while Borromini became a suicidal papal knight – a hero. And for Downes, there was something else. His father, Ralph Downes, a Catholic convert, was a distinguished organist. From a spell at the new chapel of Princeton University in the 1920s and 30s, he moved to London's Brompton Oratory, an offshoot of the Roman Oratory. He was a classicist who became an early champion of the baroque. Kerry absorbed his father's passions, and his youthful love of architecture was centred at first on Wren, Hawksmoor and Vanbrugh, before travel led him in the late 1940s to Rome and to Borromini.

"What struck me as I came to know Borromini," says Downes, "is how practical he was. I come from a family of artists and engineers, farmers and builders. My great-grandfather was a locomotive designer; from them I can see that he was far from mad. His book on the Oratory goes into great detail on the ways he designed burglar-proof rooftops, privies – 'made with much art' – as hygienic as they could be for the time, rooms shaped to prevent breezes blowing out processional candles . . ."

Rivals, polemicists, anti-Catholics, architects and historians did their best for centuries to thrust a sword through Borromini's reputation. Today, he is recognised as one of the greats – an architect who gave us classicism with passion, experimentation, movement, prayer and sensuality.

Borromini's Book by Kerry Downes is published by Oblong Creative for £54 www.oblongcreative.co.uk