In 837 a fleet of sixty longships sailed up the River Liffey and raided churches, forts and dwellings, including presumably those at Dublin. Later in the same year, a certain Saxolb (Söxulfr), chief of the foreigners, was killed in Brega by the Uí Colgain, a branch of the Cíanachta Breg. The Chronicon Scotorum and the Annals of Clonmacnoise ascribe the first taking and possession of the Danes in Dublin to this year. But this was only a foretaste of things to come. In 841 the Vikings returned to Dublin, this time not as raiders but as conquerors. They seized the ecclesiastical settlement at Duiblinn and established a longphort, or naval encampment, nearby; where precisely is still a matter of debate, but the present site of Dublin Castle is a likely candidate, as it overlooked the Black Pool (Duiblinn, from which the city of Dublin takes its name), which would have served as a natural harbour. Four years later the Annals of Ulster refer also to foreigners at Áth Cliath; this may simply be a loose reference to the settlement at Duiblinn, but it is possible that the native settlement of Áth Cliath was also seized and a second longphort established on the Liffey - possibly at Usher's Island. These settlements were temporary wintering camps () and probably amounted to little more than pirate bases. From their new base in Dublin, the Vikings plundered many territories in Leinster and the Midlands as far as the Slieve Bloom Mountains. Many more raids were to follow. In 845 the Vikings of Dublin plundered Dún Masc (Rock of Dunamase in County Laois), killing the abbot of Tír dá Glas (Terryglass in County Tipperary) and other dignitaries; other ecclesiastical settlements plundered in the same year included Kildare, Clonenagh, Kinnitty (County Offaly), Killeigh, Kells, Monasterboice, Duleek, Swords and Finglas. In 845 they also set up an encampment near Tullamore.