They had built a wooden bridge over the Tiber, and a great point of interest to the town was that this bridge should be kept always in good order, so that at any moment troops could pass over it. Then, with the special genius of the Romans, of which we have other instances, they ordained, curiously enough, that the men who were a corporation to take care of that bridge should be sacred; that their function, necessary to the defence of the town, should be considered holy; that they should be priests, and the highest of them was called "the high bridge-maker." So it happened that there was in Rome a corporation of bridge-makers, _pontifices_, of whom the head was the most sacred of all Romans, because in those days his life, and the life of his companions, was deemed necessary to the safety of the town. Things changed; very soon Rome was large enough not to care about the Janiculum; very soon Rome conquered a part of Italy, then the whole of Italy, and finally almost the whole of the world. But when once something is done in Rome, it remains done; when once a thing is said, it remains said, and is repeated; and thus it happened that the privilege of the bridge-makers' corporation, as beings sacred and holy, remained; and that privilege made everybody respect them; gave them a sort of moral power. Then kings wanted to be made High Bridge-makers; after kings, consuls; later, dictators; and, later, emperors themselves made themselves High Bridge-makers, which meant the most sacred persons in the town.