22. With Tiberius' absence, Augustus relied solely on Gaius and Lucius to be his heirs. Lucius Caesar died in 2 AD at the age of 18 of an unspecified sudden illness. Of what did Gaius Caesar die in 4 AD?
From Quiz Roman Emperor: Life and Reign of Tiberius
Answer:
Infected wound
When Gaius Caesar's wound claimed his life in 4 AD, Augustus was left with no choice but to adopt Tiberius as his son, who therefore became his successor.
Lucius suddenly became ill in in Massilia, Gaul, in 2 AD while he was on his way to Hispania to meet the Roman Army. The same year, Gaius invaded Armenia, which had been invaded by the Parthians. He was tricked into meeting the leader of the Parthian rebels in Armenia, under the pretense of the two just having a conversation. Gaius was stabbed, but not killed. Accounts differ as to where he was stabbed. Gaius did not think his wound was too concerning, and continued to fight in Armenia.
One year later Gaius was weakened and ill by the wound, and did not wish to take any further part in public life. Augustus tried to rekindle his interest in being the emperor one day, but this was to no avail. Gaius died in a small town in what is now Turkey in 4 AD.