Grotesque

The word "grotesque" comes from the Italian "grottesco" meaning "of, or pertaining to a cave".  The caves in question were the antiquities from Roman times, especially Nero's Golden House, the Domus Aurea, which by the Middle Ages had been covered over and buried  by later buildings and improvements in the city, their rooms becoming "caves" the later inhabitants of Rome could climb down to to explore and wonder at.
The paintings that remained from Roman times, containing the wonderful and incongruous, gods, men and animals of fantastic shapes and forms, led to the word "grottesco" meaning "bizarre" and "unusual".

Thus pass away the glories of the world - sic transit gloriae mundi - from gold encrusted domes of the Golden House to subterranean caves visited by bats and vacationing spelunkers.

And at the time of Nero, the Christian community worshiped underground in the catacombs, subterranean tombs. As the evidence of Rome subsided beneath the ground, the Faith resurrected from the catacombs.

That is irony: the change of fortunes; a paradox of the Canticle of the Virgin as the Mighty are cast from their thrones.