 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.