Originally, a short verse composition, constructed so that one or more sets of letters (such as the initial, middle, or final letters of the lines), taken consecutively, form words. An acrostic in which the initial letters form the alphabet is called an abecedarius. Ancient Greek and Latin writers, medieval monks, and Renaissance poets are among those who devised acrostics. Today the term is used for a type of word puzzle utilizing the acrostic principle. A popular form is double acrostics, puzzles constructed so that the middle or last, as well as initial, letters of lines may form words.