One of the many ancient Roman ruins atop the Palatine Hill is the Domus Augustana, part of the huge Flavian Palace, built for Emperor Domitian.
The Domus Augustana – sometimes called the Domus Augustiana – was the luxurious residence of the emperor (his official name was Titus Flavius Domitianus, hence the name of the palace). The palace complex was built in the late 1st century, and the Domus Augustana was lived in by emperors until about the third century. It's fairly well-preserved.
The ruins on the Palatine Hill are open to the public starting at 8:30am, with the closing time varying from 4:30pm-6:30pm depending on the season. A 48-hour combined ticket that includes the Colosseum, Forum, and Palatine Hill costs €12. Children under age 18 are admitted for free, and there's free admission the first Sunday of every month.