These sources, while they offer evidence for the importance of Fergus Mór in Medieval times, are not evidence for his historical career. Indeed, only one king in the 6th century in Scotland is known from contemporary evidence, Ceretic of Alt Clut, and even this identification rests upon a later gloss to Saint Patrick's "Letter to Coroticus". The first kings of Dál Riata whose existences are reasonably sure are Fergus's grandsons Gabrán mac Domangairt and Comgall, or perhaps his great-grandson Áedán mac Gabráin.