What role does alliteration play in strong-stress Old English poetry?

In Old English poetry, alliteration serves as a fundamental structural principle rather than a decorative element. It acts as the primary mechanism for linking the two halves of a line, which are separated by a medial pause known as a caesura.123

The typical Old English line consists of four strong stresses, with the caesura dividing the line into two hemistichs (half-lines). The role of alliteration within this structure is as follows:34

• Linking Mechanism: One or two stressed syllables in the first half-line must alliterate with the first stressed syllable of the second half-line.1
• Accent Requirement: Alliteration must fall on accented (stressed) syllables; unaccented syllables do not count toward the pattern, even if they begin with the same letter.1
• Structural Governance: Along with strict rules regarding accent and quantity, this alliterative pattern provides the governing rhythm for the verse, which is measured by the count of stresses rather than the number of syllables.14

This system was normative for Old English heroic and lyric poetry, maintaining a consistent formal structure for centuries.34