Kent’s Horse Guards replaced a lovely old jumble of buildings that had grown so rotten that the coaches of the Royal family could not pass under its gateway lest masonry fell upon them. It is shown in the picture by Canaletto that Lord Lloyd-Webber paid £9.2 million for in 1992. (It’s on show at the Tate until next Sunday. Note the tiny figure of a man peeing against the outside wall of David Cameron’s rose garden, a need better catered for today by the efficient Olympic organisers.)  More restrained than Horse Guards’ “restless” skyline (as Pevsner calls it) is the serene Queen’s House, Greenwich, chosen as the scene for dressage and suchlike horsey arts. Built by the man whom Kent worshipped, Inigo Jones, it was finished in 1635, decades before Greenwich Hospital, which Wren had the sensible genius to centre on the small white building, framed, in the view from the river, by receding colonnades.  The river has come into its own in the Games, as it did at the Jubilee. London usually turns its back on the Thames. It is invisible from the Strand or from our one grand processional way, the Mall (which deserves an Olympic gold of its own). But crowds at the equestrian cross-country events at Greenwich looked down from the hill of the Observatory and meridian, over the wide Thames to that remarkable view of London with the blighted bankers’ Canary Wharf in the foreground, masking the Olympic Park in the faraway Lea Valley.  The Thames, sweet Thames once more, now the fish have returned, runs softly from the lake at Eton Dorney, under 37 bridges, past Hampton Court’s chimneyed film-set (where Wiggins triumphed) and curves past the Embankment. Here the marathon runners will on Sunday pass the modest memorial to Joseph Bazalgette, who built it, with useful sewers beneath. “Flumini vincula posuit,” it says in funny writing: “He put the river in chains.”  We saw during the women’s marathon what a good idea it was to put the route through the dear, dead Sunday streets of the City. The runners strode through the curiously attractive arcade of Leadenhall Market (glimpsed in a Harry Potter film), which many people never get round to seeing. It’s on the site of the Roman forum. Indeed, the marathon route is a serious history lesson, taking in the Monument (from which the libel blaming the Papists for the Great Fire was removed a mere 182 years before the Games) and reaching its halfway point below Bow Bells in Cheapside, where Becket’s father bought a house 900 years ago, next to Ironmonger Lane, as it was called then and still is.  The crowds and television viewers won’t be able to see what isn’t there – the tragedy of London’s fine buildings bombed by enemies, lost in fires, worse, torn down by 19th-century money-grubbers and stupid modern planners in league with architects. Of Wren’s 51 City churches, seven were lost in the Blitz, but 14 had been demolished by the Victorians for economic reasons.  I had thought that the Olympics would sink the beauties of London in a tawdry maze of crowd-control meshing and vending points. I was wrong. The buildings stand out poignantly in the watery sunshine. London emerges as a living city, its heart beating faster for the Olympics.
It&rsquo;s rakey, rakey time at Horse Guards, then a marathon tour of the City&rsquo;s   historic streets