In Greek and Roman mythology, Ascanius was the son of Aeneas and Creusa. After the Trojan War, as the city burned, Aeneas escaped to Latium in Italy, taking his father Anchises and his child Ascanius with him, though Creusa died during the escape. Ascanius later fought in the Italian Wars. Virgil's Aeneid says he had a role in the founding of Rome as the first king of Alba Longa.
According to another legend mentioned by Livy, Ascanius may have been the son of Aeneas and Lavinia and thus born in Latium, not Troy. Thirty years after the founding of Lavinium, Ascanius founded Alba Longa. He had a son or grandson called Aeneas Silvius.
Ascanius was also called Iulus or Julus. The Gens Julia, or the Julians, the clan to which Julius Caesar belonged, claimed to have been descended from Ascanius/Iulus, his father Aeneas, and, ultimately, the goddess Venus, the mother of Aeneas in myth, his father being the mortal Anchises.
The name Iulus was popularised by Virgil in the Aeneid: replacing the Greek name Ascanius with Iulus linked the Julian family of Rome to earlier mythology. The emperor Augustus, who commissioned the work, was a great patron of the arts. As a member of the Julian family, he could claim to have three major Olympian gods in his family tree: (Venus; Jupiter; and Mars), so he encouraged his many poets to emphasize his supposed descent from Aeneas.
Ascanius, in the Aeneid, first used the phrase "annue coeptis," the root phrase of what later became a motto of the United States of America.