A pontist has few theories to consider, only two, indeed, and these are sisters. Let me introduce you to them. [Illustration: A BROKEN WAR-BRIDGE OF THE XIII CENTURY, AT NARNI IN ITALY; REPAIRED WITH WOOD] II STRIFE AND HISTORIC BRIDGES The first theory sets thought astir on the necessity of having landways and waterways which in all respects are fitted to distribute the many functional activities of military and civil life. It is not enough that a complex type of society should have many intricate systems of circulation for its multiform traffic. The weakest points in each system ought to be regarded as danger zones in the strategy of national defence, so it is a duty to protect them from attack, and the protection should be as complete as the military arts can make it, age after age. Now the most vulnerable points in a system of landways are the long bridges by which roads and railways are conducted across wide chasms, and deep valleys, and perilous waterways. Yet in England, and in other countries also, neither roads nor railways are defended; indeed, modern bridges are not only unfortified, but as sensitive to bombs as elephants are to large bullets. Why has the world forgotten that a powerful nation whose bridges were cut would be like a giant whose arteries were severed? As the suffragettes burnt down Yarmouth pier, so a conspiracy of civil disorder, acting in accordance with a well-formed plan, could in a night, with a few sappers, cripple a vast railway, by blowing up the main strategic bridges. I am giving a chapter to this urgent subject, most engineers having evaded with equal zest the charm of beauty and the security of our food supplies. At a time when the nations overarm themselves for war, tradesmen and engineers have erected ugly bridges for an imagined peace; but now that the art of flying threatens civilization from overhead and from all around, like a new Satan, the public attitude to highways cannot remain lethargic. Willingly or unwillingly, we must recall and renew those principles of defensive war with the help of which bridges were safeguarded by the Romans and also in the Middle Ages. Frank Brangwyn has painted many aged fortified bridges, making a most varied selection; and in each of these historic pictures he illustrates the attitude of old times to the theory of pontine defence.