A line of iambic hexameter (i.e. twelve syllables divided into six feet of iambic stress pattern). The Alexandrine being a long line, it is often divided in the middle by a pause or caesura into two symmetrical halves called hemistiches. Pope’s Essay on Criticism offers this exemplary comment on the Alexandrine: “A needless Alexandrine ends the song / That, like a wounded snake, drags its slow length along.” Alexandrines were common in French poetry from the twelfth century onwards; indeed, they derived their name from a French poetic sub-genre written to extol the merits of Alexander the Great. They were later used to brilliant effect by Racine (1639-1699), but tend to be thought unwieldy by English poets whose …
Editors. "Alexandrine". The Literary Encyclopedia. First published 01 November 2001; last revised 13 December 2004.
[http://www.litencyc.com/php/stopics.php?rec=true&UID=22, accessed 24 March 2017.]