On the northern slopes of the mountain of Flavigny (at the point marked _J C_, _Plate 25_), Cæsar had chosen the most convenient spot for observing each incident of the action, and for sending assistance to the places which were most threatened. Both sides were convinced that the moment of the decisive struggle had arrived. If the Gauls do not force the lines, they have no further hope of safety; if the Romans obtain the advantage, they have reached the end of their labours. It is especially at the retrenchments on the slopes of Mont Réa that the Romans run the greatest danger, for the commanding position of the enemy gives them an immense disadvantage (_iniquum loci ad declivitatem fastigium, magnum habet momentum_). One part of the assailants throw darts; another advances, forming the tortoise; fresh troops incessantly relieve the soldiers who are weary. All strive desperately to fill the fosses, to render useless the accessory defences by covering them with earth, and to scale the rampart. Already the Romans begin to feel the want of arms and strength. Cæsar, informed of this state of things, sends Labienus to their succour with six cohorts, and orders him, if the troops cannot maintain themselves behind the retrenchments, to withdraw them and make a sally, but only at the last extremity. Labienus, encamped on the mountain of Bussy, descends from the heights to proceed to the place of combat. Cæsar, passing between the two lines, repairs to the plain, where he encourages the soldiers to persevere, for this day, this hour will decide whether they are to gather the fruit of their former victories. Meanwhile the besieged, having abandoned the hope of forcing the formidable retrenchments of the plain, direct their attack against the works situated at the foot of the precipitous heights of the mountain of Flavigny, and transport thither all their materials of attack; with a shower of arrows they drive away the Roman soldiers who fight from the top of the towers; they fill the fosses with earth and fascines, clear a passage for themselves, and, by means of iron hooks, tear down the wattling of the parapet and the palisade. Young Brutus is first sent thither with several cohorts, and after him the lieutenant C. Fabius with seven more; at last, as the action becomes still hotter, Cæsar himself hurries to them with new reserves.