Mental discipline, prayer and remoteness from the world and its disturbing visions reduce temptation to a minimum, but they can never entirely abolish it. In medieval traditions, abbeys and convents were always considered to be expugnable centres of revolt against infernal dominion on earth. They became, accordingly, special targets. Satan, issuing orders at nightfall to his foul precurrers, was rumoured to dispatch to capital cities only one junior fiend. This solitary demon, the legend continues, sleeps at his post. There is no work for him; the battle was long ago won. But monasteries, those scattered danger points, become the chief objectives of nocturnal flight; the sky fills with the beat of sable wings as phalanx after phalanx streams to the attack, and the darkness crepitates with the splintering of a myriad lances against the masonry of asceticism.