Gaius Aurelius Valerius Diocletianus was one of the most energetic and inventive of the emperors of Rome. He reigned from 284-305 AD. The latter date is that of his retirement, not his death: uniquely among emperors, he stepped down from supreme power, and spent the last decade of his life in retirement in the palace he built for himself on the beautiful Dalmatian coast, not far from the provincial capital of Salona. Unlike most buildings from the period, the palace survived. The photo below is of the windows of the emperor's private quarters--now a bar.
Some may think this rather a sad come-down for an emperor's bedroom, but if people hadn't moved in the palace would be only another ruin. The Roman buildings which survive more-or-less intact are the ones that people kept using and therefore kept repairing; those that were not still in use were left to fall down, or, more commonly, used as a source of brick and stone by later generations. (Or, of course, the ones which were buried under volcanic ash or river silt.) Roman Salona, the one-time capital of Dalmatia, suffered that fate.
Salona--now Solin--is a very interesting site, but--to me at least--nowhere near as interesting as the palace, and a large part of that interest is the way the old building was changed by new users. What happened is this: about a century after Diocletian died, the people of Salona abandoned their city: the Avars and Croats were invading, and Salona, some miles inland, was hard to keep supplied in a siege. The palace lay on the coast: it had a good harbour, a strong defensive wall, and ample barracks which had once provided accommodation for the emperor's guards. The Salonians moved in, and, over the centuries that followed, rebuilt and adapted the complex to suit their own needs.
Some of the things they did would have outraged the emperor, had he known of them. Diocletian was a great persecutor of Christians, but the mausoleum he'd built to be buried in was turned into a church; even worse, it was dedicated to St. Domnius, who was martyred by--errm--Diocletian. The temple near the mausoleum, dedicated to Jupiter, whom Diocletian claimed as his divine father, became a baptistery--though it retains its beautiful Roman vaulting.
While we were there, the basement (now clean and tastefully illuminated) was being prepared for a flower show. The contrast between the fragile, ephemeral flowers and the old stones reminded me of the verses by Kipling:
Cities and Thrones and Powers
Stand in Time's eye
Almost as long as flowers,
Which daily die:
But, as new buds put forth
To glad new men,
Out of the spent and unconsidered Earth
The cities rise again.
This season's Daffodil,
She never hears
What change, what chance, what chill,
Cut down last year's;
But with bold countenance,
And knowledge small,
Esteems her seven days' continuance
To be perpetual.