One of the greatest theatrical studies of tyranny, revolution, and civil war, Julius Caesar is also a highly personal play — a breathless, gripping portrayal of friendships and alliances torn apart by political ambition and the intoxicating effects of power. In this production by Théâtre National de Bretagne and American Repertory Theater, French director Arthur Nauzyciel adopts the look and style of the late 1960s, when the world is in flux and the national psyche is in turmoil after President Kennedy’s assassination.