"A pamphlet of 1904," quoted by Nicholas Purcell, "The City of Rome," in Richard Jenkyns, ed., The Legacy of Rome: A New Appraisal
(Oxford: Oxford University Press, 1992), pp. 421-453 (at 449):
When Man is wholly remade as Pagan, then and only then will he be able to undertake an unerring flight towards the Future. In this spiritual palingenesis Rome as symbol of Paganism can and must have a mission. So excavate all her stones; re-erect all her columns; mark out all the traces and indications of her greatness. Those who made lime from her statues and columns for churches and palaces, monasteries and brothels, did not understand the necessities of the human spirit, of history, of social evolution.
Purcell doesn't give a more precise citation, and I can't locate the pamphlet.