This city is ancient, over a thousand years old. Sometimes the shiny slickness of it all can make me forget that: flashing through tunnels, speeding past in a blur of advertising gimmicks and fashion addicts. Walking, the city acquires depth. Layers of ancient history settle like dust around you and suddenly the glittery modern façade disappears, like the glitch it is, under the weight of time. The invisible city begins to appear. In the long street of indifferent modern buildings, a gap, a hacked-back space revealing bare bone: a grimy, narrow medieval church, a Victorian timber merchant's warehouse, faded paint on wooden doors cracked and gnarled with age.  A green space, dotted with lichened tombstones barely readable and the outline, in the grass, of thick stone walls. All hemmed in by modern monoliths and trendy warehouse apartments and brightly lit, media-infested bars: but stare for long enough at these gaps, and they merge, and the modern city disappears, for a while.

In the invisible city, my ancestors walk.

Strange that I should find myself here. Emerging from the street where my friends live I recognise the name of this street in front of me, and realise that at the end of it is the church where my grandmother Lucy was christened. A famous church, with its own history - and some of mine. Standing here now there's a multitude of connections: to the living Lucy as I knew her, to her birth in 1898, to her parents and the fifteen brothers and sisters we found listed in the parish register. They walked here, where I'm standing. They lived here, this was their home patch. In the invisible city of which they are a part, the buildings and spaces are different, and yet the same. My eyes focus inward to the fast 3d model animating in my head: the gaps in the modern buildings melt and run together as cinemas and shops and streets and churches rebuild themselves, children in flat caps and worsted play with wooden tops or hang from the backs of horse-drawn omnibuses. Unknown but familiar faces. They disappear slowly, leaving the quiet road, no people, dusty Sixties clothing factories shuttered and dark. I walk on, back in the real city, but catching echoes of them in every old wall I pass.

Later, making notes, thinking further back, of the ancestors walking in Covent Garden in 1687. Christened in St Martin in the Fields, a large Romanesque church off Trafalgar Square, where it is estimated that seventy thousand people were buried in the graveyard before it was closed. It's paved over now. It's only about six metres square - but deep. Somewhere down there, no doubt, family bones, co-existing with these living ones here, which write this, now.

The invisible city and the real one have meeting points. Sometimes I am one of them.

with thanks to the locals