The Baron d'Holbach, a prominent figure in the French Enlightenment, is best known for his writings against religion. His prolific campaign of atheism and anti-clericalism, waged from the printing presses of Amsterdam in the years around 1770, was so radical that it provoked an unprecedented public response. For the baron's enemies, at least, it suggested the end of an era: proof that the likes of Voltaire and Jean-Jacques Rousseau were simply a cabal of atheists hell-bent on the destruction of all that was to be cherished about religion and society. The philosophes, past their prime and...