Tilt: a skewed history of the Tower of Pisa by Nicholas Shrady

"I call that living architecture," wrote John Ruskin of the buildings of Buscheto di Giovanni Giudice, whose Duomo at Pisa dictated, quite precisely, the form and detail of the campanile next to it. Yet the key point about the so-called Leaning Tower is that it has been the epitome of dying architecture, a not quite vertical expectation of mortality, evident since the boggy silts around the Arno river hit the tilt button after the fourth of the tower's seven galleries was completed in the 12th century.

Is there anything in architecture more obdurately bathetic than this canted campanile? Even after being pulled back towards vertical by a crucial, and now secure, 40 centimetres in 2001, the bell-tower is still four metres out of whack - enough to continue to make us forget its essential architectural qualities.

Nicholas Shrady's otherwise admirable Tilt fails to ask why we should be so fascinated by this particular oddity. Shrady is excellent, and highly readable, on the dense machinations that dogged the construction of Pisa's 60-metre marvel; and good, too, at layering in tranches of Pisan history, and the developments that affected the Mediterranean and Middle East as the tower went up.

The contexts are relevant. When Shelley and Byron hit town in 1821, the former declared it a "large, disagreeable city almost without inhabitants". Two centuries earlier, Galileo described it as a "sad and desolate port" under the Florentine cosh. Yet Pisa had once been as great as Venice and Genoa, and its power was signalled by Buscheto's cathedral, the bell-tower, and a grandiose cemetery founded on 53 galley-loads of earth from Mount Calvary. Pisa was a potent medieval power-base whose grandeur died in 1225, when the Genoese triumphed in a 160-galley battle off Meloria.

The slumping tower suits this wider scenario. But Shrady wastes far too much time on the claim that Galileo conducted his key gravitational experiments from it. He obviously did not and, in any case, had been beaten to the proof of a fixed rate of fall regardless of the weight of objects by Girolamo Cardano, 60 years earlier.

Never mind: Shrady ferrets out some delicious morsels, noting for example that the Chinese engineer Cao Shizong, of the Slanting Building Research Institute in Hangzhou, pitched up during the city's recent search for a solution to the tilt - but refused to reveal his methods. The chapter on the final corrective measures, devised by Professor John Burland of Imperial College, is a model of concise clarity.

But has the magic gone? Is the leaning tower, suddenly, only a virtually risky experience? The "Tiltin' Hilton" that US troops came within minutes of flattening in 1944 is now frisson-free. There's one upside, though: we may, at last, begin to savour the campanile for its essential beauty, rather than its lurch.

That the book itself lurches (it is cut to form a parallelogram) is klutzy. This rather reductive marketing ploy suggests that Tilt is a "novelty read": it's far better than that, and deserves more than to be unwrapped by a few thousand brainy but eccentric uncles this Christmas.