 DATE: In "I, Claudius" Tiberius is married to Vipsania at the same  time that Julia is married to Marcellus. Historically, he didnt  marry Vipsania till 19 BC, by which time Marcellus had been dead for  four years and Julia has been married to her second husband Marcus  Agrippa for two years, with one child by him and pregnant with a  second.