Byron’s poem The Bride of Abydos (1813) begins:
Know ye the land where the cypress and myrtle
Are emblems of deeds that are done in their clime?
What deeds are these trees emblems of? What myth and folklore is Byron alluding to?
Laurel and olive wreathes commemorated deeds of greatness which immortalized their doers through the retelling of their deeds. In contrast, myrtle wreathes were given for "second tier" accomplishments, and cypress (as far as I know) was not given as a reward. These associations can be seen in both ancient and modern texts. For example, in Virgil's Aeneid, Polydorus the son of Trojan king Priam, was betrayed, murdered, and forgotten. Polydorus's corpse is overgrown with myrtle until Aeneas properly buries him. Closer to Byron's time, at a commencement address to the University of Edinburgh, Robert Leighton, Archbishop of Glasgow warned the celebrating students that their laurel crowns would be followed by cypress wreaths (emphases mine):
Were I allowed to speak freely what I sincerely think of most of the affairs of human life, even those that are accounted of the highest importance, and transacted with the greatest eagerness and bustle, I should be apt to say, Magno conatu magnas nugas,—that a great noise is made about trifles. But if you should take this amiss, as a little unseasonable upon the present occasion, and an insult upon your solemnity, I hope you will the more easily forgive me, that I place in the same rank with this philosophical convention of yours, the most famous councils and general assemblies of princes and great men; and say of their golden crowns, as well as your crowns of laurel, that they are Καπνοῦ σκιας οὐκ ἂν πριάιμην--things of no value, and not worth the purchasing. Even the triumphal, inaugural, or nuptial processions of the greatest kings and generals of armies, with whatever pomp and magnificence, as well as art, they may be set off, they are, after all, so far true representations of their false, painted, and tinsel happiness, that, while we look at them, they fly away; and, in a very short time, they are followed by their funeral processions, which are the triumphs of death over those who have, themselves, triumphed during their lives. The scenes are shifted, the actors also disappear; and, in the same manner, the greatest shews of this vain world likewise pass away. Let us, that we may lop off the luxuriant branches of our vines, take a nearer view of this object, and remember, that what we now call a laurel crown, will soon be followed by cypress wreaths. It will be also proper to consider how many, who, in their time, were employed as we are now, have long ago acted their parts, and are now consigned to a long oblivion; as also, what vast numbers of the rising generation are following us at the heels, and, as it were, pushing us forward to the same land of forgetfulness!
This tragic poem is set in the Turkish court, and much contrast is made between this Turkish setting and the protagonist Selim, said to be "Greek in soul if not in creed". Byron is bringing out the theme that this is not a place like Classical Greece, where great deeds were done and celebrated. Instead, it is an upside-down world of injustice, where acts of betrayal and mistreatment are rewarded, and where would-be heroes are unable to carry out great deeds, but instead are killed and forgotten. Byron writes The Bride of Abydos as a heroic elegy to Selim, to create a picture of someone who lived in a setting where it was impossible to become a reputed hero, but who (in Byron's eyes) represents true nobility of spirit.