Inenarrabilia sunt Dominicae incarnationis mysteria. The Sermon on the Nativity in Porto, Biblioteca Pública Municipal, Santa Cruz de Coimbra 31 (56)

This article presents the first critical edition of the pseudo-Hieronymian sermon on the Nativity transmitted by the 12th/13th century manuscript Porto, Biblioteca Pública Municipal, Santa Cruz de Coimbra 31 (56). The quotation of its incipit by the abbot Speraindeo in a letter to Paulus Albarus reveals that the sermon circulated already in the 9th century in the Iberian Peninsula under Jerome's name. The first part of the article provides a description of the manuscript and of its contents. The second part considers the context within which the sermon is transmitted, namely a series of ten liturgical sermons delivered on feast days from Advent to the Circumcision of Christ. The third part examines the sermon's sources and loci paralleli and advances some hypotheses about its origin. The most plausible of these is that it is a cento combining extracts from Ambrose's Expositio in Lucam and Chromatius' sermon 32 on the Nativity, including several hitherto unknown passages from the Chromatian homily.