Split (/splɪt/; Croatian: [splît] ^ⓘ, see other names) is the second-largest city of Croatia after the capital Zagreb. It is the largest city in Dalmatia, largest city on the Croatian coast, and the seat of the Split-Dalmatia County. The Split metropolitan area is home to about 330,000 people. It lies on the eastern shore of the Adriatic Sea and is spread over a central peninsula and its surroundings. An intraregional transport hub and popular tourist destination, the city is linked to the Adriatic islands and the Apennine Peninsula. More than 1 million tourists visit it each year.

The city was founded as the Greek colony of Aspálathos (Ancient Greek: Ἀσπάλαθος) in the 3rd or 2nd century BCE on the coast of the Illyrian Dalmatae, and in 305 CE, it became the site of the Palace of the Roman emperor Diocletian. It became a prominent settlement around 650 when it succeeded the ancient capital of the Roman province of Dalmatia, Salona. After the sack of Salona by the Avars and Slavs, the fortified Palace of Diocletian was settled by Roman refugees. Split became a Byzantine city. Later it drifted into the sphere of the Republic of Venice and the Kingdom of Croatia. For much of the High and Late Middle Ages, Split enjoyed autonomy as a free city of the Dalmatian city-states, caught in the middle of a struggle between Venice and Croatia for control over the Dalmatian cities.

Venice eventually prevailed and, during the early modern period, Split remained a Venetian city, a heavily fortified outpost surrounded by Ottoman territory. Its hinterland was won from the Ottomans in the Morean War of 1699, and in 1797, as Venice fell to Napoleon, the Treaty of Campo Formio rendered the city to the Habsburg monarchy. In 1805, the Peace of Pressburg added it to the Napoleonic Kingdom of Italy and in 1806 it was included in the French Empire, becoming part of the Illyrian Provinces in 1809. After being occupied in 1813, it was eventually granted to the Austrian Empire following the Congress of Vienna, where the city remained a part of the Austrian Kingdom of Dalmatia until the dissolution of Austria-Hungary in 1918 and the creation of Yugoslavia. In World War II, the city was annexed by Italy, then liberated by the Partisans after the Italian capitulation in 1943. It was then re-occupied by Germany, which granted it to its puppet Independent State of Croatia (NDH). The city was liberated again by the Partisans in 1944, and was included in the post-war Socialist Yugoslavia, as part of People's Republic of Croatia. In 1991, Croatia seceded from Yugoslavia amid the Croatian War of Independence.

The name Aspálathos or Spálathos may come from the spiny broom (Calicotome spinosa, ἀσπάλαθος in Greek), although it is the related Spanish broom (Spartium junceum, σπάρτος) that is common in the area.

After the Roman conquest, the name became Spalatum or Aspalatum in Latin, which in the Middle Ages evolved into Aspalathum, Spalathum, Spalatrum and Spalatro in the Dalmatian language of the city's Romance population. The Venetian name, Spalato, became official under Venetian era, in international usage by the Early Modern Period and is still the name of the city in Italian. From the 10th century onwards, the local use was Spaleto, from where, through a stage *Spəlētu- to *Splětъ, came the South Slavic forms: the ekavian Splet, ijekavian Spljet and ikavian Split. In the 19th century, following the Illyrian movement and its official recognition by the Habsburg Monarchy, the Croatian names Split and Spljet became increasingly prominent, before Split officially replaced Spljet in 1910, by decision of the city council.

Formerly, the name was thought to be related to Latin palatium 'palace', a reference to Diocletian's Palace. Various theories were developed, such as the notion that the name derives from S. Palatium, an abbreviation of Salonae Palatium. The erroneous "palace" etymologies were notably due to Byzantine Emperor Constantine VII Porphyrogenitus, and were later mentioned by Thomas the Archdeacon. The city is several centuries older than the palace.

Although the beginnings of Split are traditionally associated with the construction of Diocletian's Palace in 305, the city was founded several centuries earlier as the Greek colony of Aspálathos, or Spálathos. It was a colony of the polis of Issa, the modern-day town of Vis, itself a colony of the Sicilian city of Syracuse. The exact year the city was founded is not known, but it is estimated to have been in the 3rd or 2nd century BC. The Greek settlement lived off trade with the surrounding Illyrian tribes, mostly the Delmatae.

After the Illyrian Wars of 229 and 219 BC, the city of Salona, only a short distance from Spálathos, became the capital of the Roman Province of Dalmatia and one of the largest cities of the late empire with 60,000 people. The history of Spálathos becomes obscure for a while at this point, being overshadowed by that of nearby Salona, to which it would later become successor. The Roman Emperor Diocletian (ruled AD 284–305) in 293 began the construction of an opulent and heavily fortified palace fronting the sea, near his home town of Salona, selecting the site of Spálathos (or Spalatum in Latin). The Palace was built as a massive structure, much like a Roman military fortress. The palace and the city of Spalatum which formed its surroundings were at times inhabited by a population as large as 8,000 to 10,000 people.