The City of London's changed in shape several times over the centuries. Its perimeter was once defined by the old Roman Wall, but over the years the boundary has nudged outwards into a less regular shape which sort-of resembles Australia. For purists the Square Mile's area is currently 1.12 square miles, making it the smallest administrative district in England. And the distance around the edge I calculate to be just over six miles, which is ideal for a decent-sized walk.
Let's walk the untweaked edge first, the stretch along the north bank of the Thames. This means starting by the Tower of London, which has never been inside the City and is (obviously) part of Tower Hamlets. The City begins at Tower Millennium Pier, from which it's impossible to walk west along the riverbank because some lumpen redevelopment is in the way. Pedestrians need to retreat to Lower Thames Street, past Tower Place and Sugar Quay, which is best done swiftly. And then a proper treat, so long as the tide's out, because the first access to the Thames offers steps down to the beach. And there really is a beach here, or was between 1934and 1971, for the benefit of poor Londoners who couldn't get to the seaside. I was pleasantly surprised to discover that not all the sand has washed away, although you really wouldn't want to sit amongst the detritus left behind as the water ebbs, so best not bring your bucket and spade. An occasionally flooded walkway whisks you past HM Revenue and Customs, then there's a splendid view back to Tower Bridge from outside old Billingsgate Market. And no, Tower Bridge isn't in the City of London either.
But London Bridge is. Peculiarly the whole of London Bridge forms part of the City of London, right the way from the north bank to the south, so this walk has to nip up an unsavoury back staircase from the waterside to reach the upper span. It's a magnificent diversion via one of the finest views in London, now augmented by the Shard spearing the clouds from close by. A pair of dragons guard the southernmost extent of the City, keeping Southwark at bay a couple of hundred yards further than strictly necessary. There's nothing historic about this spot - the original London Bridge landed a few dozen metres further downstream - but it is a reminder of the medieval structure's mercantile importance.
Retreating to the north bank, modern buildings line the waterside walk in a mostly uninspiring way. The path ducks beneath Cannon Street station for sensory overload. See the snaking line of blue lights embedded in the pavement, listen to the heritage soundscape being pumped from several speakers, and try not to smell the chlorine escaping from the neighbouring gym. On the far side by the Banker pub is your second and final opportunity to walk down onto the Thamesforeshore, unless you've timed it wrong and water's lapping roughly against the steps. The next bit is Walbrook Wharf, the City's waste disposal site, where containers of smelly refuse are loaded onto barges and carted off to Thurrock. If the lights flash and the barrier goes down then the walkway closes and you'd best divert inland.
You'll have to divert soon enough anyway, beyond Southwark Bridge at Queenhithe, which is the sole remaining inlet on this northern curve of river. An underwhelming plaque reminds passers by that King Alfred established his harbour here in the late 9th century, although all you'll see bobbing here now are plastic bottles. The inland pedestrian stretch is grim, however, unless you're a fan of brutalist concrete or of dour dual carriageway diving into tunnels. Moving swiftly on. The riverbank is regained just before the Millennium Bridge swoops overhead. Be sure to investigate the glass obelisk below, its three etched sides dedicated to London's ecclesiastical, scientific and general history. Perhaps investigate the linear steel sundial nearby, but don't be distracted by the funicular railway up towards St Paul's. The Thames path then shrinks to accommodate the Blackfriars one-way system before passing first beneath the railway bridge then its highway counterpart.
Beneath Blackfriars Bridge is the outfall where what's left of the River Fleet enters the Thames, again seen only at low tide, and not without some difficulty. It's also the second point at which a diversion to the opposite bank is required, because Blackfriars Bridge is the only other London bridge that's entirely part of the City of London. To walk the perimeter of the Square Mile properly you need to walk all the way across this 150 year old bridge to the marker on the opposite side. A single dragon this time, perched without ceremony in the centre of the roadway, glaring south. The vista downstream is still blocked by construction work for the new Blackfriars station, whose midriver platforms have yet to be opened up because the solar roof isn't ready. Soon, please.
Back on the north bank we join the Victoria Embankment, the only road to pass directly along the City's Thames-side edge. It boasts twisty iron lampstands and gruff copper lions, and a succession of naval craft recommissioned as floating bars. Ground level evens out beyond Unilever HQ, and that's Inner Temple Garden approaching on the right hand side. Temple is as far west as we're going - that's the legal enclave rather than the tube station (which is resolutely part of Westminster). On weekdays you can cut up Middle Temple Lane, which is a Harry Potter-esque cobbled thoroughfare lined by legal chambers, whereas at weekends that's locked and lesser back passages await. And it's here on the Embankment that the City's 'proper' boundary dragons reside, perched on a pair of Portland stone plinths. These two heraldic beasts were relocated from the Coal Exchange in 1963, and all the other dragons around the perimeter are merely half-size copies. We'll meet more of these tomorrow...