Festus Avienus, Descr. orb. terr. 761–763, GGM ii.184
hic cum plaustra poli tangit Phoebeius ignis, nocte sub illustri rota solis fomite flagrat continuo, clarumque diem nox aemula ducit
There [at Thule], when Phoebus’ fire touches Ursa Major, under shining night the Sun’s wheel burns with continuous flames, and the night, eager to equal it, leads the bright day.