All editions and translations of Homer's Iliad present the epic as a series of twenty-four segments always marked off in the same places. In this respect the Iliad conforms to, and seems even to originate, a practice in which narratives of any considerable length are almost always presented in marked segments, usually called chapters. Similarly, dramas, except very short ones, usually run as a series of acts whose dimensions are determined in the composition (i.e., not afresh with each performance). Acts may be marked by curtains, intermissions or briefer pauses, or other variations in the performance: in ancient Greek drama the segmentation is unmistakeably marked by the placement of choral lyrics (Arist. Poet. 1452b). It is not exactly clear why the chapter and the act should be so indispensable, but authors and audiences alike know intuitively that they are. Yet many scholars since antiquity have believed that the Iliad and the Odyssey originally lacked marked segmentation, and that the now-familiar presentation was imposed upon them later by someone other than their composer(s). Even today, when few scholars see profit in analyzing the Iliad and Odyssey into earlier and later strata, the so-called 'book divisions’ continue to offer a tempting target for analytic criticism.