The Domus Aurea, or Golden House, was the sprawling palace of the Roman emperor Nero. Archaeologists recently uncovered a chunk of Egyptian blue ingot, an example of the opulence of the palace itself.

The palace is called the Domus Aurea, or Golden House, erected by and for Nero. When the 30-year-old emperor’s crazed world exploded in A.D. 68, and he ordered a subject to drive a knife through ...