At 9.17am on Saturday April 24, 1993 the City of London Police received a coded warning from the South Armagh Brigade of the IRA. Just over an hour later a bomb in a tipper truck parked in Bishopsgate and loaded with almost a ton of fertiliser was detonated, destroying adjacent buildings and severely damaging many others within a 500m radius. The cost of building repairs was estimated at £1bn.

The IRA bombing campaign set in train a series of events that led to an equally dramatic but more benign change in the architecture of the Square Mile – the rise of the Eastern Cluster. The close-kissing towers, still growing on the City skyline – once dominated by Wren’s 51 church spires – have multiplied ever since Foster & Partners received planning permission for 30 St Mary Axe in 2000 on a site made vacant by the 1992 Baltic Exchange bomb.

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