These are on the Circus Maximus side of the Palatine Hill, to the left of the Baths of Maxentius
and are at the southern end of the Hippodrome aka "Stadium of Domitian
Someone unidentifed but helpful just wrote a private to say that a tv show called "The Engineering of Rome" showed this structure and said it was an ancient shopping mall" and they may have said it was built over Nero's palace.
Thanks for the info! Any added info is welcome.