An elaborately decorated room has been unearthed at Emperor Nero's Domus Aurea (Golden House) after 2,000 years.
The Sphinx Room features lavish frescoes of panthers and centaurs, flowers and fruit, aquatic creatures, birds and the god Pan, as well as, of course, a sphinx.
Experts chanced upon it while doing restoration work on the vault of a neighbouring part of the building.
"It is the fruit of our strategy that focuses on conservation and scientific research," said Alfonsina Russo, head of the Colosseum archaeological park that the Domus Aurea belongs to. "It is an exceptional and thrilling find."
The sumptuous complex of 150 rooms was built by Nero in 64 AD, after the great fire that devastated Rome – which he is commonly, but erroneously, said to have started and fiddled his way through.
Much of it is now underground, buried by tonnes of earth on the orders of the architects of Emperor Trajan, who built luxurious baths over Nero's former palace, archaeologists said. They added that it will remain buried, due to fears for the stability of the complex.
The golden palace of the ill-famed Nero (37-68 AD) first reopened in June 1999 after 21 years in which it was Rome's best-kept secret, open only to art officials and special guests.
Around €2.5 million was spent on refurbishing rooms filled with frescoes of weird and wonderful creatures such as winged lions, griffins and tritons – the painting of which led to the coinage of the word "grotesque", from the Italian word grotto, meaning cave.
The Domus has a cherished place in Italian art history, thanks to Renaissance greats including Raphael and Michelangelo lowering themselves on ropes in order to gaze at and copy the ancient wall drawings.