Similes are a prominent feature of epithalamia, with poets comparing the bride and groom to characters from myth or to elements of the natural world. Catullus wrote two epithalamia (61 and 62), together with two other poems with marked epithalamian characteristics (64 and 68). This paper examines the question of why similes are so important to the genre of epithalamium, concentrating on Catullus 61, which is particularly rich in its deployment of comparison. The paper argues that comparison is crucial to the themes of Roman marriage: similes locate the human institution of marriage between the poles of myth and nature, and they afford a vehicle for considering the way marriage links together the disparate terms of male and female.It has long been recognised that Catullus is an aficionado of the simile form: as Richard Hunter puts it, 'Catullus, more perhaps than any other Roman poet, seems to have seized the opportunities for self-conscious experimentation which the simile form offered.'1 The important study of Svennung (1945) charted the corpus, pointing out in the process interesting patterns of clustering and absence. There are only three similes in the polymetrics (2b, 7.3-8, 17.18-21), and only two in the epigrams (72.3-4 and 97.7-8); 2 developed similes clump in the longer poems, specifically in 61, 62, 64, 65 and 68. 3 It is significant that all these simile-rich poems share an intense interest in the theme of marriage as focused through the moment of the wedding. 4 Svennung already remarked *