 Ossory was a small kingdom wedged between the larger realms of Munster and Leinster.At the beginning of his reign in the 840s, Cerball's allegiance was pledged to the over-king of Munster, but as that kingdom grew weaker Ossory's strategic location allowed opportunities for his advancement.Cerball had previously fought against the Vikings, but he allied with them to challenge the supremacy of Máel Sechnaill and his Norse-Irish allies.