Final answer:
Augustus did not use monthly speeches in the forum as a method to promote his achievements; instead, he issued coins, constructed monuments, and hosted entertainments.
Step-by-step explanation:
The method that Augustus did not use to advertise his achievements and solidify his rule in the minds of the Romans was giving monthly speeches in the forum.
Augustus utilized various methods to communicate his power and the prosperity he brought to the Roman Empire.
These methods included issuing coins with his likeness and symbolism that reinforced his authority, commissioning and constructing monuments throughout Rome to celebrate his achievements, and hosting grand entertainments such as chariot races and gladiatorial shows to win over the masses and exhibit his benevolence as a leader.
However, there is no historical evidence that suggests he gave monthly speeches in the forum as one of his regular practices for propaganda.