The old gasholder did not need to do anything to hold a place in the mind. It only had to stand there, a circular cage above the railway line or beside the ring road, too large to be street furniture and too empty to feel like a building. I still think of them as a kind of municipal weather: always present, never quite addressed, turning the skyline into something that had machinery in its bones.

Their actual purpose was plain enough. Gasholders stored town gas, then became redundant as coal gas gave way to North Sea natural gas, with gas increasingly moved and stored through pipelines. Historic England's short introduction to gasholders puts the major demolition wave from about 2000 onwards. The BBC gives the earlier turn: by the 1990s, most local gas networks could run at full capacity without them, and the decision to start demolishing them came in 1999.

That should make the story tidy. A technology becomes unnecessary, the land is valuable, the structure comes down. However, gasholders were never only containers. MOLA calls them the last visible remains of the former town-gas industry, and that phrase has the right discomfort in it. Last visible remains. Not the industry itself, not even the useful part of the industry, but the part that kept catching the eye from train windows and cricket grounds and backs of buses.

National Grid owned around 500 gasholders across 350 sites, and in 2013 it earmarked 76 for redevelopment. The same year, according to The Guardian, Southern and Scottish Gas Networks proposed removing 111 more over 16 years. The numbers are large, but the loss is oddly local. Nobody misses "500 gasholders." They miss the one that told them the train was nearly home, the one by the Tesco, the one at the edge of the ground that seemed to breathe behind the commentary.

King's Cross has the grand version of survival. Gasholder No. 8, built in the 1850s at St Pancras Gasworks, was decommissioned in 2000, dismantled in 2011, refurbished in Yorkshire, and returned in 2013 as the frame around a public park. The neighbouring frames now hold apartments. At Kennington Oval, Lambeth's own project page says a Grade II listed gasholder will be restored, with flats built inside the frame as part of the Oval Gas Works redevelopment. This is preservation, yes, but with a very London aftertaste: the ghost kept because the address can afford to keep it.

I don't mean that as a simple complaint. Reuse is better than scrap, and a public park inside a Victorian iron circle is not nothing. Still, there is something awkward about turning industrial voids into lifestyle geometry. The hollow part mattered. The BBC piece gets close to it when it says memory alone is not the impressive thing, but the size and the void of space. A plaque can remember a function. It cannot replace the feeling of a town having one huge empty lung above it.

That is why the gasholder belongs beside other obsolete structures I've been circling lately: the dead logic of the pedestrian underpass, the railway extension at Barking Riverside, even the stranded military apparatus at Stenigot. Each one leaves a different kind of residue. The underpass keeps moving bodies through a plan nobody quite believes in. Barking Riverside is infrastructure arriving before its habits. The gasholder is stranger because its absence has volume. A demolished tower can still mark a place by making the sky look newly cheap.

There was a time, not very long ago, when a town announced itself through things that were not trying to be seen. Water towers, cooling towers, chimneys, gasholders: accidental heraldry, visible because the work had to happen somewhere. Now the replacement skyline is better rendered, more profitable, less embarrassing. I can see why councils prefer it. I can also see why the old frames, dramatic for all their emptiness, keep looking more truthful after the gas has gone.

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