Diocletian's Palace

Where it sits. Diocletian's Palace is not a building that a town grew around; it is the town. The complex occupies a rectangle of roughly 215 by 180 metres on the waterfront of Split, its southern wall once rising straight from the sea and now facing the Riva promenade. Around 30,000 square metres are enclosed, the southern wall stands up to 26 metres high, and some three thousand people still live inside the Roman perimeter, in houses built into, on top of and out of the imperial fabric over seventeen centuries. Nowhere else in Europe is a late Roman imperial residence still in continuous domestic use.

Built for a retirement. Diocletian, born nearby at Salona, was the emperor who divided the Roman world into a tetrarchy and then did something no emperor had done before: he abdicated, on 1 May 305, and retired. The palace was raised for that retirement between roughly 295 and 305, part fortified camp and part villa. Four gates pierced the walls — the Golden Gate to the north on the road to Salona, the Silver to the east, the Iron to the west, and the Brass Gate at sea level on the south, through which a boat could be brought almost to the door. Two colonnaded streets crossed at the centre. The northern half held the garrison, servants and stores; the southern half was the emperor's own, arranged around the Peristyle, the sunken ceremonial court where he appeared to those admitted. Twelve sphinxes, already fifteen centuries old when they arrived, were shipped from Egypt to decorate it; one black granite figure still sits intact beside the Peristyle.

Two conversions. Diocletian's octagonal mausoleum, ringed by columns and roofed with a brick dome, became in the seventh century the Cathedral of St Domnius — dedicated to a bishop of Salona whom Diocletian's own persecution had killed, which makes it perhaps the most pointed act of architectural reuse in Christendom. It is the oldest cathedral building still in use as such anywhere. Across the court, the Temple of Jupiter became the baptistery, keeping its coffered barrel vault of interlocking stone blocks and acquiring an eleventh-century font carved with a Croatian king. The Romanesque bell tower beside the cathedral was begun in the twelfth century, finished much later, and largely rebuilt in 1908 after its stonework failed.

On screen. The palace's basement halls — the substructures built to level the sloping ground and carry the imperial apartments above — served as Meereen in Game of Thrones. These vaulted chambers, cleared of centuries of accumulated waste only from the middle of the twentieth century, appear in the fourth-season finale as the catacombs beneath the Great Pyramid where Daenerys chains Viserion and Rhaegal, and they return in the fifth season for Meereen's throne room and the spaces beneath it. The rooms were shot with very little alteration: the raw grey vaults, the puddled floors and the shafts of light from above are the actual condition of the undercroft. The pyramid itself and the Meereenese skyline are digital, and the city's exteriors were filmed at the Fortress of Klis, thirteen kilometres inland.

What you actually see today. The substructures are entered from the Riva through the Brass Gate; the central corridor running up to the Peristyle is free to walk and lined with stalls, while the great halls either side are ticketed and worth the fee, because their plan is a direct negative image of the vanished apartments overhead. Above ground, the Peristyle functions as a café and a stage; the cathedral can be climbed via the bell tower, a steep open stair with an exceptional view over the Riva and Marjan hill. The Golden Gate carries Ivan Meštrović's oversized bronze of Bishop Gregory of Nin, whose polished toe has been rubbed to a shine by people wishing on it.

Getting there and timing. Split's ferry port, bus station and railway station sit within five minutes' walk of the southern wall, and the airport at Kaštela is about half an hour away. The palace quarter is car-free but far from step-free: the lanes are polished stone, frequently stepped and often narrow, and the substructures involve a ramp and uneven floors. Summer crowds concentrate between mid-morning and late afternoon; early mornings and the hours after nine at night, when the Peristyle is lit and largely local, are the two times the place feels like the town it actually is.