The article discusses the first unwavering attack by a man of the cloth against sodomy (understood, on the contrary to the use of the term in earlier sources, exclusively as homosexual behaviour). This attack was delivered in the form of a treatise entitled 'Liber Gomorrihianus', written by the outstanding Church reformist Peter Damian. Prior to Damian no Christian writer condemned homosexuality in such resolute terms; more than that, the problem of such practices within the Church itself was seldom touched upon in the ecclesiastical literature. The treatise is characterised in the context of Damian's efforts against violating of celibacy and sexual purity by priests and monks. The contents of the treatise are also set against the background of earlier norms to be found in early-medieval penitentials, which contain a wide array of different punishments for such trespasses: e.g. mutual masturbation and oral sex between men was castigated less severely, while anal sex was considered greater abuse. Damian holds a much stricter stance. He calls for depriving all priests and monks of their offices and even of clerical status for any kind of homosexual contact (or even masturbation). For Peter Damian sodomy is the worse kind of offence possible. He states that even copulating with animals is not so terrible and dangerous, because in such cases only one soul is condemned, while in the case of a homosexual intercourse with a person of the same sex the sodomite obliterates another person. Sodomy, concludes Damian, can be compared with no other form of sin: it is death to the body and annihilation to the soul; it closes the gates to heaven. It seems that on the whole 'Liber Gomorrhianus' is devoted more to Damian's anxieties, his fears that the world is being threatened by heteronormativity, than to homosexual practices. Moreover, as the analysis of the treatise demonstrates, this menace concerns not only the sphere of sexuality, but human culture in the broad understanding of the term and social order.