Vespasian (; Latin: Vespasianus [wɛspasiˈaːnʊs]; 17 November AD 9 – 23/24 June 79) was a Roman emperor who reigned from AD 69 to 79. The fourth and last emperor who reigned in the Year of the Four Emperors, he founded the Flavian dynasty that ruled the Empire for 27 years. His fiscal reforms and consolidation of the empire generated political stability and a vast Roman building program.

Vespasian was the first emperor from an equestrian family and only rose into the senatorial rank as the first member of his family later in his lifetime. Vespasian's renown came from his military success; he was legate of Legio II Augusta during the Roman invasion of Britain in 43 and subjugated Judaea during the Jewish rebellion of 66.While Vespasian besieged Jerusalem during the Jewish rebellion, emperor Nero committed suicide and plunged Rome into a year of civil war known as the Year of the Four Emperors. After Galba and Otho perished in quick succession, Vitellius became emperor in April 69. The Roman legions of Roman Egypt and Judaea reacted by declaring Vespasian, their commander, the emperor on 1 July 69. In his bid for imperial power, Vespasian joined forces with Mucianus, the governor of Syria, and Primus, a general in Pannonia, leaving his son Titus to command the besieging forces at Jerusalem. Primus and Mucianus led the Flavian forces against Vitellius, while Vespasian took control of Egypt. On 20 December 69, Vitellius was defeated, and the following day Vespasian was declared emperor by the Senate.Little information survives about the government during Vespasian's ten-year rule. He reformed the financial system of Rome after the campaign against Judaea ended successfully, and initiated several ambitious construction projects, including the building of the Flavian Amphitheatre, better known today as the Roman Colosseum. Through his general Agricola, Vespasian increased imperial expansion in Britain. Vespasian is often credited with restoring political stability to Rome following the chaotic reigns of his predecessors. After he died in 79, he was succeeded by his eldest son Titus, thus becoming the first Roman emperor to be succeeded by his natural son and establishing the Flavian dynasty.