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There are ancient monuments, and then there are ancient monuments that people never left. Diocletian's Palace in Split is the second kind. Built as a retirement complex for a Roman emperor in the late third century AD, it has been continuously inhabited for 1,700 years. Today, around 3,000 people live within its walls, in apartments carved out of Roman rooms, medieval towers, and Renaissance additions. Restaurants occupy imperial cellars. A cathedral stands inside the emperor's mausoleum. A UNESCO World Heritage Site that is also, in the most literal sense, someone's home.
This is the complete history of Diocletian's Palace — from its construction under one of Rome's most powerful emperors, through its transformation into a medieval city, to its rediscovery by Enlightenment architects and its current status as one of Europe's best-preserved ancient monuments.
To understand the palace, you have to understand the man who built it.
Gaius Aurelius Valerius Diocletianus was born around 244 AD in Salona — the Roman provincial capital located a few kilometres from the site of his future palace, near present-day Solin. His origins were humble: ancient sources suggest his father was either a scribe or a freed slave. He rose through the Roman military during a period of extraordinary instability — the Crisis of the Third Century — when the empire cycled through emperors with lethal speed (over 50 claimants to the throne in a 50-year period, many of whom lasted months before being assassinated or killed in battle).
Diocletian survived where others didn't. He was proclaimed emperor by his troops in 284 AD, after the mysterious death of Emperor Numerian. He then defeated and killed his co-emperor Carinus the following year, becoming sole ruler of Rome.
What followed was one of the most significant reigns in Roman history.
Recognising that the empire had become too large and too unstable for one man to govern alone, Diocletian invented something new: the Tetrarchy, or "rule of four." In 285 AD, he appointed Maximian as co-emperor (Augustus) in the west. In 293 AD, he added two junior emperors (Caesars): Galerius in the east and Constantius Chlorus in the west.
The empire was divided into administrative regions, each with its own court, military, and administration. It was a radical restructuring — an acknowledgment that the traditional Roman model of a single all-powerful emperor had failed, and that pragmatic decentralisation was the path to stability.
It worked, for a time. Diocletian's reign of 21 years was the longest since Augustus, and he ended it on his own terms — the first Roman emperor to voluntarily abdicate.
Diocletian's legacy is complicated by the Great Persecution, launched in 303 AD — one of the most severe and systematic campaigns against Christians in the empire's history. Churches were destroyed, scriptures confiscated, and Christians required to sacrifice to Roman gods or face imprisonment, torture, or execution.
The reasons for the persecution are debated. Diocletian was deeply conservative in religious matters, committed to traditional Roman polytheism. His co-emperor Galerius is thought to have pushed for the more extreme measures. Whatever the causes, the historical irony is pointed: the man who persecuted Christians built the mausoleum that would eventually become Split's cathedral, dedicated to a Christian saint.
Construction of the palace began around 295 AD and took approximately ten years. The site was chosen carefully: close to Diocletian's birthplace, facing the Adriatic Sea, positioned on a small peninsula that provided natural defensive advantages.
The palace is enormous by any standard. It covers approximately 3 hectares (30,000 square metres) and is enclosed by walls up to 2 metres thick and 17–26 metres high. The southern wall, facing the sea, was more palatial in character — with a gallery of 42 arched windows overlooking the Adriatic. The northern, eastern, and western walls were more military in nature, reflecting the palace's dual character as both imperial residence and fortified garrison.
The overall plan is a modified Roman castrum — the standard layout of a Roman military camp. Two main roads (the Cardo and Decumanus) intersect at the centre, dividing the complex into four quadrants:
The southern half was the imperial residential area. The northern half housed the garrison, servants, and support staff. It was, in essence, a small city built to house one man and the apparatus required to serve him.
The stone came mostly from the island of Brač — the same white limestone that would later, supposedly, be used in the construction of the White House in Washington DC. Granite columns were imported from Egypt. Marble came from Greece and elsewhere in the empire.
The labour force included both free workers and slaves. Construction at this scale required enormous logistical organisation — quarrying, shipping, skilled craftsmanship, and coordination across hundreds of workers over a decade.
The palace had four main gates, each oriented to a cardinal direction and each named for a metal in later tradition:
The Golden Gate was the most ceremonial, with two projecting towers, elaborate sculptural decoration (most now missing), and a passageway designed to impress arriving dignitaries. Diocletian would have entered through it for the first time in 305 AD.
On May 1, 305 AD, Diocletian did something no Roman emperor had ever done: he resigned.
In a ceremony at Nicomedia (in present-day Turkey), he removed his imperial purple robe and handed power to his Caesar Galerius. His co-emperor Maximian abdicated simultaneously in Milan. Diocletian retired to his palace in Split.
Ancient sources preserve a famous anecdote. When his former colleagues urged him to return to power during the subsequent political chaos, Diocletian reportedly replied: "If you could show the cabbage that I planted with my own hands to your emperor, he definitely wouldn't suggest that I replace the peace and happiness of this place with the storms of a never-satisfied greed."
He spent his final years gardening, receiving visitors, and watching his carefully designed Tetrarchy collapse into civil war from a safe distance. He died in the palace around 311–313 AD. His precise date and cause of death are unknown.
The palace served its original imperial function for only about 170 years after Diocletian's death. It passed through various hands under the late Roman empire and was used as an administrative centre, military base, and occasional imperial residence.
The transformation came in the 7th century.
In the 610s AD, Avar and Slavic tribes swept through Dalmatia, destroying Salona — the regional capital that had stood for centuries a few kilometres away. The surviving population fled south and took refuge inside the massive walls of Diocletian's Palace.
This was the moment the palace became a city.
The refugees adapted the imperial structures to domestic use. The grand colonnade of the southern gallery became a street. The subterranean cellars, originally used for storage and as a support structure for the imperial apartments above, were built over and forgotten. The Peristyle — the great ceremonial courtyard — became the town square.
The most dramatic transformation was Diocletian's mausoleum. Originally an octagonal domed building where the emperor had intended to be worshipped after death (the Romans routinely deified their emperors), it was converted into a Christian cathedral in the 7th century.
The conversion was probably an act of practical necessity — it was the largest and most structurally sound building available. But the symbolism was irresistible: the man who had persecuted Christians, his very tomb repurposed as a church. A Christian bell tower was added in the 13th century. Today it still stands: the Cathedral of Saint Domnius, the oldest Catholic cathedral in the world that remains in its original building.
Through the medieval period, Split grew steadily within and around the palace walls. New buildings filled the spaces between Roman structures. Medieval towers rose on top of Roman foundations. The four main streets of the Roman layout remained in use, their basic geometry preserved by the buildings erected over them.
By the 13th century, Split had outgrown the palace walls and began expanding beyond them. The area immediately outside the western gate became the commercial centre — today's People's Square (Narodni Trg). But the palace remained the heart of the city, and the continuity of its use kept the Roman structure largely intact beneath later accretions.
By the 18th century, the palace had been so thoroughly absorbed into the medieval city that its Roman origins were partially obscured. It took an architect from Scotland to bring it back to international attention.
In 1757, Scottish architect Robert Adam arrived in Split with a team of draughtsmen and spent five weeks systematically measuring and documenting the palace. The result was Ruins of the Palace of the Emperor Diocletian at Spalatro in Dalmatia, published in London in 1764.
The book was a sensation. Adam's precise drawings revealed the palace's original Roman design beneath centuries of later construction, and his analysis of its architectural details — particularly the way Roman and later styles had blended — directly influenced the development of Neoclassical architecture across Britain and Europe. The "Adam style" that shaped Georgian interior design owed a significant debt to his studies at Split.
The publication also established the palace as an object of serious scholarly interest. Subsequent researchers built on Adam's work, gradually reconstructing the original appearance of the complex from the physical evidence remaining within the inhabited city.
In 1979, the Historic Centre of Split with the Palace of Diocletian was inscribed on the UNESCO World Heritage List. The designation recognised the outstanding universal value of a monument that has been "continuously inhabited since it was built" — unique among ancient Roman structures of comparable scale.
The UNESCO status brought both resources and challenges. Restoration work has been ongoing since the 1970s, working carefully to preserve Roman, medieval, and later fabric together rather than attempting to "restore" the palace to any single historical moment. The result is what you see today: layers of history visible simultaneously, a palimpsest of 1,700 years of human habitation.
Approximately 3,000 people live within the palace walls. The Peristyle is a café terrace. The Cathedral of Saint Domnius — Diocletian's mausoleum — holds regular masses. Boutique hotels occupy Roman rooms. Restaurants fill the cellars. Art galleries and shops line the medieval streets.
The palace is what it has always been: a place where people live. That's what makes it different from every other ancient monument of comparable importance. It was never abandoned. It was never purely preserved. It was used, adapted, built over, and built within, continuously, for seventeen centuries.
The best way to understand this layering — to see the Roman palace beneath the medieval city, and to comprehend what Diocletian actually built here — is to see it as it was. The Time Walk VR walking tour does exactly that: an 80-minute guided experience through the palace using augmented reality to reconstruct the original Roman structures on the actual sites where they stood.
You stand in the Peristyle and see the temple facade as Diocletian saw it. You walk through the Golden Gate and understand why it was designed to impress. You see the throne room as a throne room, not as the apartment block it later became.
Planning your visit? See our complete one-day itinerary for Split.
Want to see Diocletian's Palace as it looked in 305 AD? Book your Time Walk VR tour in Split.