The term "palace" is a misnomer. What we have is really an enormous enclosure, a sort of Roman camp. The area is trapezoidal; in other words, the sides vary in length. The north or landward side, which is the longest, has a length of 700 feet. The circuit is about half a mile, and it consumes the better part of half an hour to work your way around it. There could, of course, be no question of roofing over such a space. The whole area was divided into four approximately equal squares by two great passages, one thirty-six feet broad, leading from the water gate on the south side called the Silver Gate, through which the imperial barge used to sail into the palace, to the Golden Gate on the north side, the other running from the Iron Gate on the west to the Bronze Gate on the east. The first of these ways is interrupted near the south end by the imperial house itself. The enclosing wall was fifty feet high at its lowest part, and was seventy-five feet high near the sea where the ground fell off, so that all the buildings, sacred and profane, distributed within were hidden from view to outsiders. Not only did the imperial family, but courtiers and menials, making a population of some thirty thousand, have quarters here.
The builder and occupant of this palace was the greatest personality of the Cæsars after Marcus Aurelius, whom in military and administrative force he greatly surpassed. Entering the service as a simple legionary, he rose by slow degrees of service in all parts of the empire under various nonentities of emperors, until at Chalkedon, in 284 A.D., the soldiers proclaimed him emperor. There is a legend that a Druid priestess had prophesied to him when he was serving in Belgium under Aurelian that he would become emperor immediately after killing a boar. It is said that he saw the fulfilment of this prophecy when the Emperor Numerianus was assassinated at Chalkedon by a certain Aper (_i.e._, boar), whom he immediately struck down, exclaiming, "I have killed the boar." Of course there are those who think that the legend grew out of the name of the assassin. Diocletian's name will ever be associated with the last and most wide-reaching and systematic persecution of the Christians; but this policy was most likely forced upon him by the fanaticism of his colleague, Galerius. At this time the Roman Empire had become too bulky to be well administered by one man, however able and conscientious, and of his own accord he associated others with himself in the imperial power, confining himself entirely to the eastern part. Two years after he had issued at Nikomedia, in 303 A.D., his edict of persecution of the Christians, the cares of office weighing too heavily upon him, he laid aside the purple, retired to Salona, and began building this palace about four miles distant from it. When his withdrawal was so sorely felt that he was importuned to resume the imperial power, he declined, referring to the sweet peace which he enjoyed among his cabbages at Salona. There can be little doubt that the reason which influenced him to choose Salona as his place of retirement was that it was his birthplace, although the Montenegrins hold that they have the true birthplace in Doclea, not far from Cettinje.