The city of Split on the Croatian coast was built on the palace of the late Roman Emperor Diocletian. Or should I say built in - because the sixty-foot walls of that expansive compound, 500 by 600 feet, bounded the medieval city for hundreds of years. Dark Ages refugees from a nearby town fled to the well-preserved fortress and in time filled in the open spaces with narrow, tall houses and cramped streets. The temple of Jupiter and the mausoleum became a church and a cathedral.
I have just been to visit this postapocalyptic triple-exposure of Roman, Medieval and Late European Touristic. In the central square, former Peristyle of the palace, a rococo cathedral tower overlooks ruined columns and healthy arches. A faceless black granite sphinx from Egypt, as old to Diocletian as his ruins are to us, passes silent judgment on the grimacing heraldic lions carved on the cathedral columns.
Behind that archway is built Diocletian's split-level (sorry, but that is the mot juste) private apartments, the lower, vaulted chambers mirroring the upper works.
In his day these dungeons were flooded with a higher sea level, and his private boats floated past the pillars. As they dried, they filled with twelve feet of garbage from the dwellers above. Now they are excavated and impressive.
And what might dwell in these forgotten chambers beneath the crowded city? Balkan folklore abounds in monsters, most appropriately the chained devil Dukljan, a memory of the works of the late Emperor (on the medieval understanding that any sufficiently advanced architecture has to come from the devil.)