Texts are not written or read in a cultural vacuum. Their ability to signify derives from and is defined by their relations to the whole corpus of pre-existing literature. Texts therefore cannot be straightforward, self-contained vehicles of their authors' intended meanings, but must be read through and within a complex cultural matrix. These are truths universally acknowledged, and the cluster of ideas that they represent is conveniently termed intertextuality. Intertextual relations can, of course, be relatively simple or complex; authors can use them knowingly or unawares, actively or inertly. Although classicists have started to use the word intertextuality only recently, they have long been aware of the notion it denotes. Classical literature is congenitally and compulsively allusive; commentaries on classical texts traditionally make a practice of accumulating parallels, albeit often without much explicit sense of their allusive weight or interpretation of its function. Allusion, however, is included in but not coterminous with intertextuality: an allusion is something an author makes, deliberately, perhaps decoratively, perhaps with profound meaning; intertextuality is a property of texts when actuated by their readers, and not necessarily consciously deployed by their authors; it may relate to a specific intertext, but equally to a more general literary praxis.