John H. Middleton, Henry S. Jones and Francis M. Crawford, 1911 Encyclopædia Britannica, Volume 23… (1911)
“ The enormous vaults of the great thermae, the basilica of Constantine, and the like, cover their spaces with one solid mass like a metal lid, giving the form but not the principle of the arch, and thus allowing the vault to be set on walls which would at once have been thrust apart had they been subjected to the immense leverage which a true arched vault constantly exerts on its imposts. ”
