I don't see that a single line can constitute a stanza, although it can constitute a whole poem.
James FentonAt four lines, with the quatrain, we reach the basic stanza form familiar from a whole range of English poetic practice. This is the length of the ballad stanza, the verse of a hymn, and innumerable other kinds of verse.
James FentonFree verse seemed democratic because it offered freedom of access to writers. And those who disdained free verse would always be open to accusations of elitism, mandarinism. Open form was like common ground on which all might graze their cattle - it was not to be closed in by usurping landlords.
James FentonPoetry carries its history within it, and it is oral in origin. Its transmission was oral.
James Fenton