Damiens' Bed of Steel
R. F. Damiens, in 1757, attempted the life of Louis XV. He was taken to the Conciergerie; an iron bed, which likewise served as a chair, was prepared for him, and to this he was fastened with chains. He was then tortured, and ultimately torn to pieces by wild horses. (Smollet: History of England, v. 12, p. 39.)
The uplifted axe, the agonising wheel, Luke's iron crown, and Damiens' bed of steel.
Goldsmith: The Traveller (1768).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894