On Christmas Eve 1924 St Paul’s Cathedral was served with a Dangerous Structures notice and was closed for public safety. This talk recounts the extraordinary story of how the Cathedral moved and cracked testing the structure and relations with the City of London. It will look at the superfluity of advice that became available, the investigations which were carried out and the ingenious engineering endeavours that rendered the building safe once more. This talk is by Robert Bowles, Structural Engineer.