How was Augustus related to Julius Caesar?

The family tree

Caesar had two sisters, both called Julia, because Roman daughters took the family name. One of them married Marcus Atius Balbus, a senator from Aricia, in the hills near Rome. From there the line runs straight to the first emperor:

• Julia, Caesar’s sister, married Marcus Atius Balbus.
• Atia, their daughter, married Gaius Octavius, a rich man from Velitrae and the first of his family to sit in the Senate. He rose to praetor and governed Macedonia.
• Gaius Octavius, their son, was born in Rome on September 23, 63 BC: Caesar’s great-nephew.
• Octavia, his sister, would later marry Mark Antony.

So Augustus was the grandson of Caesar’s sister. Roman writers often call Caesar simply his uncle, but great-uncle is exact.

Growing up in Caesar’s shadow

The boy lost his father at four, and Atia remarried, to Lucius Marcius Philippus, who would be consul in 56 BC. At about twelve Octavius gave the funeral speech for his grandmother Julia before the Roman people. Caesar noticed him. At about sixteen he received military prizes at Caesar’s African triumph, though he was too young to have fought, and Caesar raised his family to patrician rank. When Caesar went to Spain to fight Pompey’s sons, the young man followed, barely recovered from illness, shipwrecked on the way and crossing roads held by the enemy. Suetonius says that won Caesar over. In 44 BC he was studying at Apollonia, across the Adriatic, waiting to join the war Caesar planned in the East.

What the will said

Caesar wrote his last will in September 45 BC and left it with the chief of the Vestal Virgins. It named three grandsons of his sisters as heirs: Gaius Octavius to three-quarters of the estate, Lucius Pinarius and Quintus Pedius to the rest. At the very end Caesar adopted Octavius into his family and gave him his name.

Why him? Caesar had no son to inherit. His only legitimate child, his daughter Julia, had died in 54 BC. The boy the Alexandrians called Caesarion, little Caesar, is not in the will, and Caesar’s friend Gaius Oppius even wrote a book denying the child was his. In 30 BC, after Actium, Octavian had Caesarion killed; Plutarch says an adviser warned him that too many Caesars was not a good thing.

Becoming Caesar’s son

Adoption by will was unusual, so Octavius made it stick step by step. He took the name as soon as Caesar’s soldiers at Brundisium hailed him as Caesar’s son, declared his acceptance before the city praetor in Rome, and in 43 BC, consul at nineteen, had it ratified by the ancient assembly of the curiae. That vote, Appian suggests, mattered because it gave him a son’s full rights over Caesar’s many rich freedmen. He was now Gaius Julius Caesar; historians call him Octavian only to keep the two apart. Antony mocked him as a boy who owed everything to a name. Augustus remembered it his own way:

At the age of nineteen, on my own initiative and at my own expense, I raised an army by means of which I restored liberty to the republic, which had been oppressed by the tyranny of a faction.

When the Senate declared Caesar a god in 42 BC, his heir became divi filius, son of the deified one, and stamped it on his coins. In the Res Gestae he calls Caesar simply “my father.” How he used that name to become the first emperor is its own story. The family habit outlived them both: Augustus had no son either, only a daughter, Julia, and in AD 4 he too passed on his power by adoption, to his stepson Tiberius.