Architect John Soane recognised the ephemeralness of London's buildings. In 1830 he commissioned draughtsman Joseph Gandy to create an imagined view of his Bank of England in a state of desolation. Though part vanity project – Soane likening his work to the ruins of ancient Rome and Greece – the commission also showed the architect knew that however magnificent his blueprints were, someday they'd be reduced to rubble. Over the centuries, many great London structures have been wiped off the map. A few of them remain as ruins.
Among the most important structures in the city's history, London Wall was built by the Romans in the late 2nd or early 3rd century, and subsequently helped keep marauding Picts, Saxons and Vikings at bay. London Wall is a palimpsest of a ruin; each generation added its own modifications (gates, crenellations, etc.), right through until the 18th century. Most of London Wall has now disappeared, but vestiges can still be seen at the Museum of London, Barbican, London Wall (the road, that is), St Alphage Garden, and Tower Hill, as well as in the basements of numerous buildings. Perhaps the most evocative remains, pictured above, can be found in the courtyard behind the Grange City Hotel on Coopers Row (near Tower Hill).
See also: Head into Merrill Lynch's alleyway just north of Newgate and you'll find a plaque and textured paving marking the route of the wall. Other plaques can be found in the Aldgate subway and around other parts of the perimeter, and the Old Bailey has some impressive remnants in its basement (not open to the public).
Animal fighting, public executions and the occasional gladiator? We don't know for sure what Roman Londoners got up to in the amphitheatre on the site of today's Guildhall, but it was no doubt a site of mass entertainment. The underground ruins here comprise the stone wall bases and remains of the drainage system. The parts of the amphitheatre that no longer exist have been recreated, bafflingly but brilliantly, in the style of the original Tron film. Step out into Guildhall Yard to see the curve denoting where the amphitheatre would have stood.
See also: London's Roman ruins are extensive and continue to be excavated today. Two other must-sees are the occasionally open Billingsgate Roman Bath House (picture) and The Temple of Mithras, though the latter is currently in storage awaiting a return to its original location.
Lesnes Abbey, in the Borough of Bexley, was built as a flamboyant apology. Richard de Luci commissioned it in 1178 as penance for complicity in the murder of Thomas Becket. Racked with debt for much of its existence, Lesnes Abbey's fate was sealed during the Dissolution of the Monasteries. Despite its unhappy time as an abbey, the ruins themselves are fascinating, in that they still accurately outline the layout. Certain window and door arches remain intact too.
The Blitz was, of course, a ruinous time for London in general. In its aftermath, the city understandably wanted to erase it from memory, and most damaged buildings were either torn down outright or, in some instances, rebuilt. St Dunstan-in-the-East is a rare exception. The church's spire was put there by Christopher Wren after the previous church was destroyed in the fire of 1666. Though St Dunstan-in-the-East was gutted during the Blitz, the spire remained intact, and renovation was ruled out. Since the early 1970s, St Dunstan-in-the-East has been a rather peaceful public garden: Hitler unknowingly created a sanctuary for City workers to eat their Meal Deals in.
See also: Christ Church Greyfriars. Just a mile away from St Dunstan-in-the-East, this church was also rebuilt by Wren, bombed in the second world war, and transformed into a garden. The spire, incredibly, is a private residence.
Blackfriars Railway Bridge
The russet pillars — sometimes referred to as 'Old Stumpy' — thrusting up from the Thames once supported the first Blackfriars Railway Bridge. Now they look altogether odd alongside the subsequent structure, which lies immediately to the east. Indeed, one row of pillars was incorporated into the side of the new-look rail bridge when it was overhauled last year. Perhaps the remaining uprights of Joseph Cubitt's 1864 design could be put to use as additional Fourth Plinths? Or could there be a place for them in the design of the touted Garden Bridge? On second thoughts, they're the most impressive visible ruins in the Thames of central London, and should stay just so.
See also: Broad Street Viaduct (which we've previously suggested might be a candidate for a London High Line). And let's not forget the dozens of crumbling ghost stations dotted all over the Underground network.
There's something ineffably creepy about the ruins of Crystal Palace. Maybe it's the noseless sphinxes and headless statues. Or it might be the resident crows, constantly making noises like someone being exorcised. The Crystal Palace (a name coined by Punch) was moved to Sydenham from its original setting in Hyde Park in 1854. It became so iconic that the area adopted the name, as did the local football team. In 1936, tragedy struck, when fire burned the Crystal Palace to the ground. Though there's talk of an ersatz 'palace' to take its place, the eerie ruins will always be the true legacy of one of the Victorians' most magnificent buildings.
See also: Winchester Palace in Southwark. This ruin was once an actual palace, and a vital cog in the workings of medieval London.
London is full of fleeting ruins — buildings that have been vacated and/or partially restored, and have not yet been regenerated. (Although these days regeneration doesn't hang around for long.)
The Heygate Estate was fully vacated in 2012 and — for a brief moment in time — Tim Tinker's controversial 1970s community development became the quintessential contemporary London ruin. Far from being abandoned, it enticed filmmakers, street artists and community gardeners. It's now a building site once more.
See also: To see what's currently crumbling, we recommend you do a Derelict London tour.