What melody does the introduction to “Don't Tread on Me” on Metallica's Black Album interpolate?

The introduction to “Don't Tread on Me” on Metallica's Black Album interpolates “America” from West Side Story.

The melody was composed by Leonard Bernstein for the musical West Side Story. Metallica used it as the opening figure of the song, creating a brief connection between the band’s heavy-metal arrangement and one of the best-known American musical-theater scores.

“Don’t Tread on Me” takes its title from the motto associated with the Gadsden flag, whose snake also appears on the album cover. That shared imagery helps explain why listeners sometimes connect the song’s introduction with patriotic music, even though the melody comes from Bernstein’s musical rather than from a national anthem.

The track was sent to rock radio after the album’s release but was not issued as one of the album’s five commercial singles. The official singles were “Enter Sandman,” “The Unforgiven,” “Nothing Else Matters,” “Wherever I May Roam,” and “Sad but True.”