Like Diocletian's Palace in Split, the palace in Gamzigrad was designed to be a representative Imperial residence, housing the abdicated Emperor while retained the imperial symbols.
Archaeological excavations in the fortress revealed remains of a palace with exceptionally fine mosaics, baths and impressive gates. Among the important finds from the site are portraits of rulers made from the
Egyptian purple stone called porphyry and coins that help to date the complex.
Felix Romuliana is a UNESCO World Heritage Site. Among the reasons why it is a protected site is the fact that the complex is preserved in its integrity and authenticity up to now unlike many other buildings.
Sources:
https://www.worldheritagesite.org/
https://www.atlasobscura.com/
https://whc.unesco.org/