The premier bell of Oxford is Great Tom. Since 1684 it has hung in the tower of Christ Church, the most monumental constituent college within the University of Oxford, and every evening at five minutes past nine precisely it strikes 101 times, providing the city with a figurative tocsin.

Why 101? Because in 1546, when the college was founded, there were 100 members of the Christ Church foundation. Yes, but why 101? Oh, because in 1663 an additional student was co-opted. Why is it rung? Because in 1684, when the bell went up, the gates of the college were closed at 9 p.m. Well then, why five past nine? Because in those days, Oxford being located 1 degree 15 minutes of longitude west of the Royal Observatory at Greenwich, 9:05 p.m. Greenwich Mean Time was 9:00 p.m. in Oxford.

And why does it still ring like that, when Christ Church today has some 650 scholars and students, and local times have not applied in England since the 19th century? Ah, well...read on.

Oxford is the oldest university in the English-speaking world. By general consent it is one of the most distinguished, and it is not much like any other. As it would say of itself, it is sui generis—one of a kind. I have known it all my life, as a schoolchild, undergraduate, graduate and finally as an honorary fellow of my college, and I have reached the conclusion that its character depends upon an equilibrium so improbable that it amounts to an ethos all its own.

For one thing, Oxford sits in the middle of a fairly ordinary mercantile and industrial city, very unlike the ideal civic setting of Cambridge, England; Princeton, New Jersey; or Salamanca, Spain. For another, its buildings are a baffling jumble of structures ancient and modern, with no obvious center to them, no dominating campus or architectural pattern. And most crucially, to my mind, Universitas Oxoniensis is unique in its attitudes: eager modernity beside medieval loyalties, skepticism tempered by tradition, and the whole venerable entity spiced with anomalous quirk and absurdity.

Recently the Congregation, the university's governing body, contemplated a change in its ancient statutes that would have, for the first time, allowed outsiders to form a majority in Oxford's policymaking body. Perhaps it was hoped that a few more rich tycoons in the management might help with the raising of money for the university—which, by comparison with its American counterparts, is pitifully underfunded. I suspect it came as a relief to most Oxonians when the proposal was defeated, and the old place remained, as far as is possible in a modern unified state, master of its own affairs. But might it not mean, some asked, that old fogies of Congregation would be united in defending a general status quo? But no, the truth is that, except in matters like the eccentric ringing of bells, the university is so tangled an institution, riven by so many different purposes and even ideologies, that its corporate instincts are likely to be at least as radical as they are stick-in-the-mud.

For the members of Congregation include the heads of the university's constituent colleges, and there are 39 of them—at the moment (new ones often crop up). This makes for permanent creative discord. Each college is autonomous, with its own statutes, its own agendas and its own proud master, warden, president, provost, rector or dean. The prime loyalty of most Oxford alumni is not to the university but to one's college—"What college?" is the first thing any Oxford graduate says to another when they meet in boardroom or on battlefield in later life. Not so long ago it was a socially loaded inquiry, because some colleges used to be more fashionable than others, like fraternities or sororities in the United States: today inherited class has lost most of its insidious allure, even in England, even at the University of Oxford, where Stan Laurel achieved such instant and fulsome respect when (in A Chump at Oxford, 1940) a window fell on his head and temporarily transformed him into a peer of the realm.

The all-pervasive collegiate structure of the university powerfully complicates its affairs. If the colleges are no longer graded by social distinction, they still represent a bewildering range of aesthetic, financial or intellectual reputations. Some are very rich, owning country estates, lavishly endowed by patrons of long ago. Others, notably the former women-only colleges, bravely scratch a living, compulsorily helped along by their richer colleagues (perhaps reluctantly, too, for was it not an Oxford savant who told the female sex, in 1884: "Inferior to us God made you: and our inferiors to the end of time you will remain"?).

Built over the course of nine centuries, huggermugger amid the medieval lanes of the inner city, or spilling out toward the open country, the colleges are also an idiosyncratic display of architectural history. They are all jumble, all enclaves of privacy and style, the older ones, indeed, actually fortified against potential louts or religious zealots. To wander around them, sometimes chivied away by officious college porters, sometimes spontaneously befriended by fellows of the Royal Society, under forbidding gatehouses, up and down venerable staircases, through a mesh of quadrangles, amid the miasmas of a dozen dining halls—to wander through those 39 colleges is to feel oneself stumbling through a separate world of idiosyncrasy.

But rationality keeps breaking in. Without it, of course, the equilibrium would collapse, and the University of Oxford would limp along as a mere nostalgic relic. In fact, the place is in a constant state of flux.

Between the two world wars, Oxford's architecture was largely stagnant, and almost the only beautiful contemporary structure was a little footbridge over the river Cherwell. A spirit of change was signaled in 1959 when Danish architect Arne Jacobson was commissioned to design the new college of St. Catherine's, on the outskirts of the medieval center among the water-meadows to the east. He did the whole thing from scratch, from pepper shakers to bicycle racks, in purest Scandinavian Modern, the dominant style of the day.

This was bold and exciting, but not very Oxford—it lacked the requisite elements of humor and intricacy. Fortunately for my instincts, though, over the years since then the university and its colleges have been developed in a more properly muddled manner. This has been dictated, of course, not by ethos but by the exigencies of finance, planning restrictions and social progress. A sprawling new science area appeared. A particle accelerator building arose above the topsy-turvy rooftops. Where there was once an old electrical power station, there is now a laboratory housing several wind tunnels. Another brand-new college, all glass and pebble dash, arose beside the Cherwell north of the old center. A big new law library materialized on one flank of the city; on the other flank, by the railway station, a Syrian-born multimillionaire sponsored the Said Business College, with a tower like a ziggurat.

Sidling in among the labyrinthine purlieus of the colleges too, sundry lesser new constructions gently remind us now that, despite its reputation, nothing in Oxford really stays the same. Squeezed between quadrangles may be a concrete dormitory, half-hidden behind a Georgian block, a modernistic new library. Put together all the buildings of Oxford that have been added during the past few decades and you would have an elegant new university of its own, complete with all faculties.

And through it all swarms a multitudinous cross section of contemporary humanity. Some 40,000 students are at large at Oxford, if it is term time, half of them from the university itself, half from the assorted educational establishments that flourish in its shadow. Another 149,000 townspeople jam the brassy shopping malls of the commercial center, and what seem to be a thousand buses from a hundred different companies parade the noble High Street. Some innocent visitors, expecting an idyllic haven of youth and contemplation, take one look at the city center and drive hastily away. Matthew Arnold called Oxford a sweet city of dreaming spires. No longer: it is a maelstrom of varied energies, the very antithesis of tradition's ivory tower.

But so it should be, to my mind, if a university is to reflect the full range of human energy—to be, for better and for worse, a microcosm of its culture. And at the heart of it all anyway, invested by suburbs and industrial quarters, Universitas Oxoniensis pursues as always its majestically ambiguous and perhaps unconscious purpose—to remain its esoteric self but to be a vital part of the great world too.

The head of one of the greatest colleges admitted to me recently that the world had defeated him, and he could no longer cope with the relentless criteria of a modern university. It was the dreaming spires for him, and he presently retreated into a gentler field of scholarship. In a harshly competitive age, Oxford has to sell itself, and shiny indeed are the brochures, lavish the functions, flattering the honorary degrees and fellowships, endless the hospitality of such college heads, by which it solicits the means for its survival.

But survive it does. This truly remarkable engine of contemporary intellect is still able, after roughly 900 years, to attract scholars of rare distinction, students of grand promise, from the four corners of the world. A third of the University of Oxford's students, in the year 2007, come from abroad, representing 139 different countries: and there are still sufficient men and women of genius who are so attuned to the particular mores of this strange place that all the gold of the Indies cannot lure them elsewhere.

How does it work? God knows. The University of Oxford is such a tangle of discrete influences and loyalties, so loaded with separate authorities, so littered with boards and customs and councils and faculties and electors and visitors and trustees that picking one's way through it is like exploring a labyrinth. But work it does, and I like to think that its particular combination of the radical and the nostalgic, the dogmatic and the ecumenical, the ironic and the opportunist, the earnestly sensible and the antic illogical is what gives the place not only its ethos but its resilience.

Think of this. The most distinguished graduate college at Oxford is All Souls, founded in 1438 and popularly alleged to number among its Fellows the cleverest men and women in England. Once in every hundred years this eminent company celebrates something called the ceremony of the mallard, when it commemorates the fable of a wild duck supposed to have flown out of the foundations when the college was being built. After a good and vinous dinner those academics perambulate the premises looking for the shade of that bird, carrying sticks and staves, led by a Lord Mallard in a sedan chair with a dead duck on a pole, climbing to the roof and singing a gibberish song—Ho, the blood of King Edward, by the blood of King Edward, it was a swapping, swapping mallard.

When in 2001 they celebrated the ceremony of the mallard for the umpteenth time, they printed a booklet about the occasion. On its cover they quoted a contemporary commentator (me, as it happened!) to the effect that no event in Europe could be sillier, "not the most footling country frolic or pointless Anatolian orgy."

Inside the booklet, though, Oxford being Oxford, the Lord Mallard of the day confidently looked forward to the duck's resurrection "in future centuries."

Jan Morris, who lives in Wales, has written some 40 books on travel and history, including Oxford (1965).