It has been said that the taking of a fortress depends primarily on the making of a good plan to take it, and the proper implementation and application of the resources to make the plan work. Long before a fortress has been besieged and conquered, it has to have been outthought before it can be outfought. This book outlines some of the more successfully thought out sieges, and demonstrates why it is that no fortress is impregnable. A siege can be described as an assault on an opposing force attempting to defend itself from behind a position of some strength. Whenever the pendulum of technology swings against the "status quo," the defenders of a fortification have usually been compelled to surrender. We must stay ahead of the pendulum, and not be out-thought long before we are out-fought, for, as it will be shown in this book, "no fortress is impregnable."