Prophecy, cosmology and the natural world are at the center of the Vita Merlini, Geoffrey of Monmouth's c. 1148–50 poem that further develops his Merlin character made famous in the Prophetiae Merlini and Historia regum Britanniae (De gestis Britonum). Throughout the poem, Merlin's prophetic abilities seem connected to the natural world, and his knowledge extends to scientific observations on the cosmos. He is frequently at odds with life in the court, always preferring to return to the wilderness. This pains his sister, Ganieda, and her husband, Rodarchus, who beg him to come back to their kingdom. At one point, Ganieda attempts to dissuade him from his woodland sojourn by reminding him about the inconveniences of winter. In response, Merlin asks that she build him a very particular house (among other buildings):

This request makes narrative sense: in response to his sister's concern about surviving the winter in the woods, Merlin asks for a place in which he can pass the harsher months in comfort while still observing the heavens to make his astrological prophecies. The detail of seventy windows and seventy doors, though, is oddly specific, even for a poem that revels in the marvellous. This specificity has interested readers of the poem, but its meaning and source have proven elusive. In this brief article, we will propose that a previously unidentified analogue may hold the key to Geoffrey's source: the tenth-century Middle Irish Saltair na Rann (‘The Psalter of the Quatrains’).