Actually, I don't know if he did use the words "tidal wave", but he does refer to paganism in a very expressive way. Here it is, taken from "The City of God", Book 12:
"This life of ours—if a life so full of such great ills can properly be called a life—bears witness to the fact that, from its very start, the race of mortal men has been a race condemned.
Think, first, of the dreadful abyss of ignorance from which all error flows and so engulfs the sons of Adam in a darksome pool that no one can escape without the toll of toils and tears and fears. Then, take our very love for all those things that prove so vain and poisonous and breed so many heartaches, troubles, griefs, and fears; such insane joys in discord, strife, and wars; such fraud and theft and robbery; such perfidy and pride, envy and ambition, homicide and murder, cruelty and savagery, lawlessness and lust; all the shameless passions of the impure—fornication and adultery, incest and unnatural sins, rape and countless other uncleannesses too nasty to be mentioned; the sins against religion—sacrilege and heresy, blasphemy and perjury; the iniquities against our neighbors—calumnies and cheating, lies and false witness, violence to persons and property; the injustices of the courts and the innumerable other miseries and maladies that fill the world, yet escape attention."Quite a good definition of paganism, don't you think?