THE T OWER MIGHT HAVE ENDURED forever with very little upkeep, had it not been for a nasty infestation of humans. From a janitorial standpoint, the problem with this particular race was not that they were de- , but avidly con -structive, and would on no account leave off bringing new building-stuff in through the all-too-numerous gates, and fashioning them into shelters. Left to the elements, such improvisations would break down naturally in decades or centuries, leaving the Tower as God and the Normans had intended it to be. But the difficulty with a human was that where he found a shelter he would occupy it, and when it broke, fix it, and if not prevented, build annexes onto it. To the management of the Tower, it was less an infestation of termites than a plague of mud-daubing wasps.