Metabolism was an architectural movement that emerged in Tokyo in 1960 and thought of the city as a living organism: infrastructure as skeleton, building units as cells that are renewed. In a country destroyed in war, growing fast and sitting on a seismic belt, it proposed changeability rather than permanence.

The Nakagin Capsule Tower, completed by Kisho Kurokawa in 1972, is that programme's clearest realisation. One hundred and forty factory-made capsules — each 2.3 by 3.8 by 2.1 metres, a single-person living unit with bed, bathroom, storage and a circular window — were trucked into Tokyo and bolted one by one onto two concrete cores by crane. The capsules attach only to the core, not to each other; by design each could be removed and replaced without disturbing the rest. The projected life was twenty-five years.

Not one capsule was ever replaced. The cost of replacement, ownership divided among the individual units and the impossibility of agreement among the owners locked the system; as asbestos, plumbing and waterproofing problems accumulated the building became unliveable. Despite a long preservation campaign it was dismantled in 2022; some capsules went to museums and collections, one to MoMA. The lesson that remains is institutional rather than technical: designing a building to be replaceable is not enough unless the regime of ownership and maintenance that would replace it is built as well. The idea of modular, demountable building is back on the agenda today through the argument over the circular economy.