Split is the largest Dalmatian city, the second-largest urban centre in Croatia, and the seat of Split-Dalmatia County. The city is situated on the shores of the Mediterranean, more specifically the eastern Adriatic Sea, spreading over a central peninsula and its surroundings, with its metropolitan area including the many surrounding littoral towns as well. An important regional transit center, the city is a vital link to the numerous surrounding Adriatic islands and the Italian peninsula, as well as a popular tourist destination. Split is also one of the oldest cities in the area, and is traditionally considered just over 1,700 years old. However, recent archaeological research relating to the ancient Greek colony of Aspeathos (6th century BC) establishes the city as being several hundred years older. Although the beginnings of Split are usually linked to the building of Diocletian's Palace, the city was founded much earlier as a Greek colony named Aspelathos. The Greek settlement lived off trade with the surrounding Illyrian tribes, mostly the Delmatae, who inhabited the (much larger) nearby city of Salona.[citation needed] In time, the Roman Republic became the dominant power in the region, and conquered the Illyrians in the Illyrian Wars of 229 and 219 BC. Upon establishing permanent control, the Romans founded the province of Dalmatia with Salona as the capital, and at that time the name of the nearby Greek colony Aspelathos was changed to "Spalatum". After he nearly died of an illness, the Roman Emperor Diocletian (ruled AD 284 to 305), great reformer of the late Roman Empire, decided to retire from politics in AD 305. The Emperor ordered work to begin on a retirement palace near his hometown, and since he was from the town of Dioclea near Salona, he chose the nearby seaside town of Spalatum for the location. Work on the palace began in AD 293 in readiness for his retirement from politics. The palace was built as a massive structure, much like a Roman military fortress. It faces the sea on its south side, with its walls 170 to 200 meters (570 to 700 feet) long, and 15 to 20 meters (50 to 70 feet) high, enclosing an area of 38,000 m2 (9 acres). The palace water supply was substantial, fed by an aqueduct from Jadro Spring. This opulent palace and its surroundings were at times inhabited by a population as large as 8,000 to 10,000 people, who required parks and recreation space; therefore, Diocletian established such outdoor areas at Marjan hill. The palace was finished in AD 305, right on time to receive its owner, who retired exactly according to schedule, becoming the first Roman Emperor to voluntarily remove himself from office. After a few years, a group of Roman Senators came to Diocletian's palace, asking the former emperor to return to Rome and help the Empire to overcome growing political problems. Diocletian refused, and while he was showing them his garden, he told them that he could not leave his beautiful garden which he had created by his own hands. This gesture showed that he remained bound by his word to leave political life after 21 years of ruling the Roman Empire. Following the fall of the Western Roman Empire in AD 476, Spalatum became a part of the Eastern Roman Empire, also known as Byzantium. It grew very slowly as a satellite town of the much larger Salona. However, around AD 639 Salona fell to the invasion of Avars and Slavs, and was razed to the ground, with the majority of the displaced citizens fleeing to the nearby Adriatic islands. Following the return of Byzantine rule to the area, the Romanic citizens returned to the mainland under the leadership of the nobleman known as Severus the Great. They chose to inhabit Diocletian's Palace in Spalatum, because of its strong (more "medieval") fortifications. The palace was long deserted by this time, and the interior was converted into a city by the Salona refugees, making Spalatum much larger as the successor to the capital city of the province. Today the palace constitutes the inner core of the city, still inhabited, full of