If I had to choose the most interesting human I have ever met, somewhere up near the top of the list would be an elderly, rather grave taxi driver in Rome.

I forgot his name very quickly, and he is probably no longer with us, given the staggeringly evil species of cigarette he smoked. The cigarettes notwithstanding, there was a certain slightly fierce dignity about him, a bearing that seemed familiar to me. It was obvious, though, that this guarded man would not have welcomed questions about its origin.

His knowledge of the architecture and the history of Rome went far beyond what you would expect of someone whose business was other than teaching it at university level. In architecture, especially, he was not simply knowledgeable, he seemed an authoritative critic.

I was impressed by that, and I was certainly impressed by the extraordinary tour of Rome that he gave me. But what made him specially interesting was that he held a view I had never run across before - that Benito Mussolini, despite having made a couple of mistakes in his life, was a great historical figure, a hero to whom the Italian people should be forever grateful. Sig Mussolini was a man whom God had built to walk on a very large stage, he said. He was a rare man in our diminished times. He was like the great men of long ago - and I remember that he gave the examples of Julius Caesar and Napoleon.

The grand purpose of Sig Mussolini's life, he said, had been to restore Italy's fortunes on the world stage. Although it might be a little difficult to picture it nowadays, it is true that Italy was one of the poorer countries of Europe until well after the Second World War. There was certainly a job to be done in the area of fortune restoration. When the Duce was alive, according to my tour guide, anyone who looked up at the window of his office in the Palazzo Venezia in Rome could see his light burning into the small hours of the morning every night, as he laboured over the details of the restoration of the country's society and economy.

And Sig Mussolini's unfortunate fascist tendencies? "Strong men must be strong," he said, with great conviction. "He needed to be strong to accomplish those things, and we in Italy needed him to be strong for us." His collaboration with Hitler? He was silent for a moment. "Well, it was a terrible thing. He did not choose it, but it was his fate. He could not escape it." During the course of the day I spent with this man, I became so taken with his character that I very nearly took what he said on faith. Since then, I have made a point of reading - or perhaps it would be more accurate to say dipping into - all the books and articles I come across that purport to tell Mussolini's story. I have never found one whose author was prepared to be anywhere near as complimentary as my learned tour guide was.

Yet, he insisted his view was that of many Italians, especially those old enough to have lived through part of Sig Mussolini's long (from 1922 to 1945) reign. The Second World War created a powerful moral revulsion in the Western world, a revulsion that the passage of half a century and more has hardly diminished. To suggest that anything produced by the Axis powers might have been 'good', or somehow beneficial to mankind, is to invite derision. But the truth is that although much evil was done during those days, much progress was made as well. Mankind has benefited.

My tour guide made much of the effect Mussolini had had on the architecture of Rome. And although modern critics are apt to sneer at Fascist architecture for its pretension, for its heartlessness perhaps, or for what they see as its empty modernity, the buildings for which Mussolini was responsible that I was able to see were, to me, not out of place in Rome, and held their own end up remarkably well in a City so packed with treasures.

Mine is not a popular opinion. I'm not sure whether Italians felt able to say so while he was alive, but there is certainly a feeling today that the modern buildings Sig Mussolini built are incompatible with the antiquity that Rome represents. Perhaps it is true that in order to build, Mussolini had to destroy much that might have been left alone. One modern critic has described the boulevard he made from St Peter's Square (designed by Bernini), across the Tiber to the centre of Rome, like this: "By blowing out the bottom of the enclosure to make the Via della Conciliazione, Mussolini does what he can to demote Bernini's collector to an incident in a forced march of obelisks, and the church and its dome to common landmarks in the banal drama of the Fascist City." Strong words.

Sig Mussolini himself said, and I think my tour guide might have agreed, that the boulevard was constructed to honour the "conciliation" between the Vatican and the Italian government of that time, and that it was an obvious improvement over the rather strangled arrangement that it replaced. Was it worth tearing down two rows of apparently rather fine houses to do it? "You can't build anything in Rome without destroying something," my learned tour guide friend said, with a little shrug. After the Second World War, perhaps in part because of negative feelings about the programme of building that the Duce unleashed, the development of Rome came, more or less, to a halt.

But recently, it has been restarted, and Italians are agonising, once again, over the place of modernity in a City that so epitomises history as Rome. The present boom was begun in the mid-1990s by the then-mayor, Franceso Rutelli. Work was done to restore City landmarks, like Bernini's fountains and the Villa Borghese. Then, the Italian architect Renzo Piano was asked to design a vast Music Park in the Flaminio District, well north of the centre of Rome. One of the things the Duce did, when he was alive, was to destroy the Art Deco home of the orchestra of the National Academy of Santa Cecilia. He did so because he thought, mistakenly, that it had been built on top of the lost tomb of the Emperor, Augustus, something he searched for, unsuccessfully, all his life. The Music Park will be the orchestra's new, long-awaited home. It is a complex that consists of a 3,000-seat outdoor amphitheatre and three concert halls ranging in size from 750 to 2,800 seats.

As it was being built, construction workers uncovered the foundations of a small, 6th Century villa. Renzo Piano altered his design to incorporate it, and the blend is apparently successful and evocative. The architecture critic for the Los Angeles Times, Nicolai Ouroussoff, says ".the design suggests it is possible to retain fragments of historical memory even while accepting the accelerating pace of modern life. It is a notion that seeks to embrace the entire arc of human history." A mile away, London architect Zaha Hadid is building a new, very modern Centre for Contemporary Art, a building that Ouroussoff describes as a meeting place of the rigid order that Fascist architecture represents, and the sensuality of Baroque architecture. Ms Hadid feels it is the collision of conflicting aesthetic values like those that gives Rome its cultural depth.

The American modernist architect Richard Meier has two projects in Rome now under construction - the Ara Pacis museum and the Church of the Millennium. When he unveiled his design for the museum, a group of Italian architectural students attacked it because, they said, he was turning Rome into another Los Angeles (Meier designed the Getty Center there). Italy's former deputy minister of culture said it was an affront to the city's heritage. "But the real lesson of Rome," Ouroussoff says, "is that cherishing a city's historic fabric does not require repressing the creative imagination. On the contrary, all great cities grow incrementally. It is the accumulation of these cultural strata that give them their meaning. Ultimately, each age has a responsibility to imprint its own values on that legacy." Just as Mussolini did.

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