Probably an ancient Greek settlement called Aspalathos. Emperor Diocletian constructed there around AD 300 a luxurious palace in which he resided until his death and where he was buried. After his death (AD 313) the Palace was used as a residence of expelled Roman emperors and their family members (Julius Nepos).
When Salona was conquered around AD 614 by the Avars and Slavs, its citizens fled to find shelter within the walls of Diocletian's Palace. A new settlement soon developed; the former diocese of Solin was re-established already in the 7th century.
Split acknowledged the supremacy of the Byzantine emperors from AD 812 to 1069 when it was annexed to Croatia by King Petar Kresimir IV. In 1105 the city acknowledged the nominal suzerainty of Hungarian-Croatian kings, having preserved its autonomy based on its ancient municipal rights.

From 1207 the citizens elected Croatian, Hum and Bosnian feudal lords for their priors and commissioners (Duke Domald, Petar of Hum, Grgur of Bribir, Pavao and Mladen Subic, Hrvoje Vukcic Hrvatinic). In 1420 Split acknowledged the protectorate of Venice which tried to strengthen its position in Dalmatia and restrict the rights of the cities.