The Sibyl of Erythrea stands alongside Micah recalling the fact that acording to mediaval Christian thinking the coming of christ was also foreseen in the heathen world by the prohetesses known as sibyls.
Please mention this source: The Ghent Altarpiece: Panel with The Sybil of Erythrea and interior with a view of the city, by Jan van Eyck; Hubert van Eyck, collection Sint-Baafskathedraal Gent, artinflanders.be, photo: Dominique Provost, Contractuele beperkingen.