The structure was built in at least three stages between the second half of the second century BCE and the end of the first century CE, they said.
The dwelling features an atrium-cum-garden, a banqueting hall imitating a grotto, and water features.
The authorities also said an “extraordinary” mosaic in the rustic style had been found.
“This is a major discovery,” said Culture Minister Gennaro Sangiuliano.
ANSA