Jonathan Blair/Corbis

Among the objects that excavators have salvaged from Baiae are coins, architectural fragments and a barnacle-encrusted statue of Bacchus (shown here), god of wine. During his diving expedition at the site, author Perrottet ran his hands along the diamond-studded base of Baiae’s famed lighthouse and floated undisturbed across the courtyards of magnificent villas—the erstwhile homes, perhaps, of the emperors Nero and Hadrian.