Rationem pontis hanc instituit. Tigna bina sesquipedalia paulum ab imo praeacuta, dimensa ad altitudinem fluminis, intervallo pedum duorum inter se iungebat. Haec cum machinationibus immissa in flumen defixerat fistucisque adegerat--non sublicae {5} modo derecte ad perpendiculum, sed prone ac fastigate, ut secundum naturam fluminis procumberent--eis item contraria duo ad eundem modum iuncta intervallo pedum quadragenum ab inferiore parte contra vim atque impetum fluminis conversa statuebat. {10} Haec utraque insuper bipedalibus trabibus immissis, quantum eorum tignorum iunctura distabat, binis utrimque fibulis ab extrema parte distinebantur; quibus disclusis atque in contrariam partem revinctis, tanta erat operis firmitudo atque {15} ea rerum natura ut, quo maior vis aquae se incitavisset, hoc artius illigata tenerentur. Haec derecta materia iniecta contexebantur ac longuriis cratibusque consternebantur; ac nihilo setius sublicae et ad inferiorem partem fluminis oblique agebantur, quae {20} pro ariete subiectae et cum omni opere coniunctae vim fluminis exciperent; et aliae item supra pontem mediocri spatio, ut, si arborum trunci sive naves deiciendi operis essent a barbaris immissae, his defensoribus earum rerum vis minueretur, neu ponti {25} nocerent. CAESAR, _de B. G._ iv. 17. +Context.+ The year 55 B.C. appears to have been marked by a general movement in the migration of the German tribes. An advance, consisting of two tribes, the Usipetes and Tenctri, crowded forward by the more powerful Suevi, crossed the Lower Rhine into N. Gaul. Caesar drove them back across the Rhine, +bridged the river+, followed them up into their own territories, and fully established the supremacy of the Roman arms. --Allen and Greenough. [Linenotes: 5. +fistucisque adegerat+ = _and had driven them home_ (+ad+-) _with rammers_. For Plan of Bridge see Allen’s _Caesar_, p. 103. 11-14. +Haec ... distinebantur+ = _these two sets were held apart by two-feet timbers laid on above, equal_ (in thickness) _to the interval left by the fastening of the piles_ (+quantum ... distabat+), _with a pair of ties_ (+fibulis+) _at each end_. --A. & G. 17-18. +Haec ... contexebantur+ = _these_ (i.e. the framework of timber) _were covered over by boards_ (+materia+) _laid lengthwise_. +longuriis+ = _with long poles_.] +The Bridge+ (prob. near Bonn). ‘With extraordinary speed (in ten days) the bridge was completed. It was a triumph of engineering and industry.’ --W. F. B40 THE GALLIC WAR, 58-50 B.C. (4) _Cassivellaunus. Second Invasion of Britain, 54 B.C._