rivers with his men whenever there was no other mode of transit, sometimes supported, it was said, by bags inflated with air, and placed under his arms.  At one time he built a bridge across the Rhine, to enable his army to cross that river.  This bridge was built with piles driven down into the sand, which supported a flooring of timbers.  Caesar, considering it quite an exploit thus to bridge the Rhine, wrote a minute account of the manner in which the work was constructed, and the description is almost exactly in accordance with the principles and usages of modern carpentry.

[Sidenote:  System of posts.] [Sidenote:  Their great utility.]

After the countries which were the scene of these conquests were pretty well subdued, Caesar established on some of the great routes of travel a system of posts, that is, he stationed supplies of horses at intervals of from ten to twenty miles along the way, so that he himself, or the officers of his army, or any couriers whore he might have occasion to send with dispatches could travel with great speed by finding a fresh horse ready at every stage.  By this means he sometimes traveled himself a hundred miles in a day.  This system, thus adopted for military purposes in Caesar’s time, has been continued in almost all countries of Europe to the present age, and is applied to traveling in carriages as well as on horseback.  A family party purchase a carriage, and arranging within it all the comforts and conveniences which they will require on the journey, they set out, taking these post horses, fresh at each village, to draw them to the next.  Thus they can go at any rate of speed which they desire, instead of being limited in their movements by the powers of endurance of one set of animals, as they would be compelled to be if they were to travel with their own.  This plan has, for some reason, never been introduced into America, and it is now probable that it never will be, as the railway system will doubtless supersede it.

[Sidenote:  Caesar’s invasion of Britain.] [Sidenote:  His pretext for it.]

One of the most remarkable of the enterprises which Caesar undertook during the period of these campaigns was his excursion into Great Britain.  The real motive of this expedition was probably a love of romantic adventure, and a desire to secure for himself at Rome the glory of having penetrated into remote regions which Roman armies had never reached before.  The pretext, however, which he made to justify his invading the territories of the Britons was, that the people of the island were accustomed to come across the Channel and aid the Gauls in their wars.

[Sidenote:  Caesar consults the merchants.]