In 155 BCE Rome fined Athens 500 talents for the sacking of Oropus. This was a huge amount for Athens to pay, so they sent the leading philosophers of the Stoic (Diogenes), Academic (Carneades, representing what is also known as the Skeptic school), and Peripatetic (Critolaus) schools to Rome to negotiate the fine. (The Epicureans were notoriously uninterested in politics, so there was no point in asking them.) It seems they were successful in significantly reducing the fine down to about 1001, but it was also an important event in the history of philosophy as it accelerated the adoption of Hellenistic philosophy by the Romans.
Of the three, the skeptic Carneades seems to have made the biggest impression on the Romans:
During his stay at Rome, he attracted great notice from his eloquent speeches on philosophical subjects, and it was here that, in the presence of Cato the Elder, he delivered his several orations on Justice. The first oration was in commendation of the virtue of Roman justice, and the next day the second was delivered, in which all the arguments he’d made on the first were refuted, as he persuasively attempted to prove that justice was inevitably problematic, and not a given when it came to virtue, but merely a compact device deemed necessary for the maintenance of a well-ordered society. Recognizing the potential danger of the argument, Cato was shocked at this and he moved the Roman Senate to send the philosopher home to his school, and prevent the Roman youth from the threat of re-examining all Roman doctrines. Carneades lived twenty-seven years after this at Athens.
I have tremendous respect for Yanis Varoufakis, but his appeals to the Troika were nowhere nearly as effective or influential as those of Carneades before the Roman senate.