He may, at times, seem too at ease with his hierarchies. "It was," he says about the art of Ancient Greece, "without doubt, the most extraordinary creation in the whole of history. So complete, so convincing, so satisfying to the mind and the eye, that it lasted, practically unchanged, for about 600 years." "Without doubt"? "In the whole of history"? Well, why not? This is where the most interesting discussions begin, not where they end. Why shouldn't BBC viewers have the opportunity to hear and reflect on such claims? And, after all, Clark is just as clear about what he doesn't know, as about what he does. An engaging modesty ran through the series: "I don't know enough about Persian literature to say if this is true"; "I can't pretend that I've read the Principia. If I did I wouldn't understand it." He knows civilisation when he sees it, but he doesn't claim to know everything about civilisation — only what matters and what matters to him. This is, after all, Civilisation: A Personal View.

And what is wrong with confidence? At crucial moments, at the beginning and end of the series, Clark talks about the importance of confidence and energy for civilisations. "It is lack of confidence that kills a civilisation." In that extraordinary closing speech at the end of the series, he quotes Yeats (whom he had known personally). "Things fall apart, the centre cannot hold." We forget that Civilisation was filmed as tear gas was fired in the streets of Paris, as Soviet tanks rolled into Prague, as students rioted and wanted to burn down libraries in the United States. Civilisation, like the letters of Isaiah Berlin about Turgenev and liberalism written between 1968-70 and Saul Bellow's Mr. Sammler's Planet, is a key moment of doubt and uncertainty about where Western civilisation is going at the end of the Sixties. Consider Clark's closing words: "One may be optimistic, but one cannot exactly be joyful at the prospect before us."

We are wrong to mistake Clark's erudition for the confidence of a class or a culture. Throughout the series, and much of his writing, there is an unmistakable sense of pessimism, both personal and cultural. Civilisation begins not with confidence or superiority but with a profound sense of the fragility of civilisations, how easily they can collapse. He starts with Rome. "That world must have seemed indestructible. However complex and solid it seems [my emphasis], it is actually quite fragile." Is he talking about the Edwardian world of his childhood, the Thirties or the late Sixties?

And then at the end he concludes: "The trouble is that there is still no centre." The final sequence of Civilisation shows Clark closing his copy of Yeats (not a researcher's set of notes), walking into his library at Saltwood Castle, replacing the book on one of several towering bookcases and walking towards the camera, pausing only to lovingly caress a sculpture by Henry Moore, lit up as Clark opens a door and walks out. This is beautifully filmed by Michael Gill, one of the great visual sequences in the history of British television. But it is a mistake to think that this is simply a moment of confidence in art — the books, the paintings, Moore's sculpture. It is a moment of assertion in the face of doubt and pessimism. Moore but also Yeats. The greatness of modern art but also "the best lack all conviction". Clark had conviction but he also had doubts about the biggest issue of all: the power of civilisation to endure.