Question

Why does Antony begin his speech with the words "friends, Romans, countrymen"?

Answer 1

Antony begin his speech with the words "friends, romans , and countrymen" to suggest that he and his listeners all share commonalities
By saying that words, he appeal to his audiences and creating the atmosphere of solidarity between him and the audiences

hope this helps

Answer 2

He uses a technique called the rule of three. According to the rule, things that come in threes are more appealing and satisfy you more than those that do not. It is a very common occurrence in speeches.