Chapter 4 examines Aaron Copland’s Short Symphony (1931–3) in the context of Copland’s friendship with Mexican composer and conductor Carlos Chávez. Short Symphony was partly written in Mexico. Chávez suggested a title for the work, ‘The Bounding Line’, which Copland temporarily adopted, and he conducted the premiere in Mexico City in November 1934. Chávez’s title raises questions about mutuality within a border-crossing American symphonic project, as well as the place in Copland’s classicist symphony of bodily presence, dance, and Hellenic erotics. Copland’s aesthetics of balletic line and bodily motion suggest analytic paradigms of gentle mediation, interdependence, contact, and touch – paradigms that thus spoke to the grassroots pan-American climate of political solidarity across the American continent in the late 1920s and early 1930s. Yet, mobilising an aesthetics of the body to gently utopian symphonic ends in this context proves unsustainable. Copland does not return from this border-crossing encounter acquitted of the colonial charge.