This chapter examines the liturgical performance of gender, the ways in which the differences between men and women were acted out in the recurrent ceremonies of the medieval church. The liturgical commentators' explanations for this distinction played on the common association of women with sin. The moment during the mass specifically devoted to 'union, charity, peace, and reverence' within the Christian community provided another opportunity for the performance of gender difference. The order of kissing during the ritual of peace further reinforced notions of social hierarchy within the Christian community. In the early thirteenth century, Sicard of Cremona claimed that it was the 'custom of the Romans' that menstruating women not enter a church 'out of reverence'. In the twelfth and thirteenth centuries, however, as theologians and pastors began to pay greater attention to unorthodox belief, they interpreted more and more biblical references to women in terms of heresy.