Why was Augustus uncertain about who would succeed him as emperor?

Augustus was uncertain about his successor primarily because there was no clear law designating who should inherit the position of emperor. The constitutional nature of the principate established by Augustus was not inherently heritable or continuous, which created significant ambiguity regarding the transfer of power.12

To address this, Augustus trained several young men—including his nephews and grandsons—in rhetoric, diplomacy, and military skills to prepare them for potential leadership. However, his plans were repeatedly disrupted by the premature deaths of his preferred candidates, such as Lucius and Gaius Caesar. Additionally, the scandalous behavior of his daughter, Julia, and the subsequent exile of her son, Agrippa Postumus, further complicated his succession strategy.1324

Ultimately, Augustus was forced to rely on Tiberius, whom he adopted as his son in 4 CE. Although Augustus reportedly did not like him, Tiberius was the least objectionable successor remaining as Augustus grew old.32