Final answer:
Julia married Tiberius after the death of her second husband Marcellus. This was a political move orchestrated by her father, Emperor Augustus, to secure the succession and fortify the power of the Julian family line.
Step-by-step explanation:
Julia, the daughter of Emperor Augustus, married Tiberius after the death of her second husband, Marcellus. Her first husband was Marcus Claudius Marcellus, but after his early demise, Augustus arranged for her to be married to Agrippa, who also later died. Following the deaths of her first two husbands, Agrippa and Marcellus, Julia was compelled by Augustus to marry Tiberius, his stepson, to secure the succession and consolidate power within the Julian family line. This marriage further intertwined the Julian and Claudian families, a blend of lineages that would dominate Roman politics in what is known as the Julio-Claudian Dynasty.