Alliterative verse is a form of poetry written in a style guided by alliteration and the number of stresses within a line. The major element of alliterative verse is the poetic device called "alliteration," which is a repetition of consonant sounds in a line or phrase. This is in contrast to poetic verse that uses a rhyme scheme and typically includes the number of syllables within each line as the structure.
For example, the line "light and lilting, the lady leapt upon the ledge" has a clear repetition of "l" sounds in the beginning of five different words within it; alliterative verse often used similar patterns, though structured more rigidly, to create a strong organization within a poem. Alliterative verse was often used in ancient Anglo-Saxon writings, including works from the 11th Century, and enjoyed a resurgence in popularity by certain medieval poets. Classic examples of this style of poetry include Beowulf, which is one of the oldest works in the English language, and Sir Gawain and the Green Knight
Many works of poetry are created as rhyming verse, in which the use of words and phrases that rhyme is the primary structure of the poem. In something like "I saw a frog / leap on a dog / and was startled to find / it was not a log," the structure of the poem is built on a simple rhyme scheme. Each line of this short poem, other than the third one, ends in a word that rhymes. This creates a rhyme scheme described as "A, A, B, A" in which the lines designated "A" rhyme with each other.
Alliterative verse, on the other hand, uses alliteration between and within lines to create a structure and scheme throughout the poem. For example, a series of lines might be written as "The lady leapt and landed on the floor / her sword from its scabbard struck her foe." In this example, the first line uses a repeated "l" sound for alliteration, while the second line features "s" sounds. Each line ends with a word that does not continue this scheme, but between the two lines these words are alliterative.
This is a simple example of how alliterative verse can be composed, though ancient works of English and Germanic poetry often included more elaborate schemes. Stresses were important in these poems, since the stressed syllable before a vowel in a word was the sound used in alliteration. In this way, multi-syllabic words could be included, with the alliteration coming from the second syllable if it was the stressed sound. Alliterative verse can still be found in some poems, though rhyme schemes are typically more common.