atur ix ) ▁and ▁Ros m erta ▁as ▁well ▁as ▁M ith ras . ▁▁ ▁Although ▁the ▁Ga ul ish ▁language ▁had ▁mostly ▁been ▁ou sted ▁by ▁Latin ▁by ▁the ▁ 3 rd ▁century , ▁many ▁C elt ic ▁to pon ym s ▁have ▁surv ived ▁in ▁Switzerland . ▁Of ▁the ▁ten ▁largest ▁present - day ▁Swiss ▁cities , ▁at ▁least ▁six ▁have ▁C elt ic ▁pla c ename ▁et ym ologies , ▁and ▁most ▁major ▁Swiss ▁rivers ▁have ▁either ▁C elt ic ▁or ▁pre - C elt ic ▁names . ▁ ▁The ▁order ▁and ▁prosper ity ▁of ▁the ▁P ax ▁Rom ana ▁ended ▁with ▁the ▁Cris is ▁of ▁the ▁Third ▁Century . ▁In ▁ 2 6 0 , ▁when ▁the ▁Gall ic ▁Empire ▁briefly ▁se ced ed ▁from ▁Rome , ▁em peror ▁Gal li en us ▁with d rew ▁the ▁leg ions ▁from ▁the ▁Rh ine ▁to ▁fight ▁the ▁us ur per ▁In gen u us , ▁allowing ▁the ▁A lem anni ▁to ▁in va de ▁the ▁Swiss ▁plate au . ▁ ▁There , ▁cities , ▁villages ▁and ▁most ▁villa e ▁were ▁ra ided ▁or ▁s ack ed ▁by ▁mar aud ing ▁bands . ▁The ▁numerous ▁c aches ▁of ▁co ins ▁recovered ▁from ▁the ▁period ▁between ▁ 2 5 0 ▁and ▁ 2 8 0 ▁att est ▁to ▁the ▁sever ity ▁of ▁the ▁crisis . ▁ ▁The ▁Hel vet ii ▁were ▁re - dis cover ed ▁as ▁the ▁for eb ears ▁of ▁the ▁Swiss ▁in ▁the ▁early ▁histor i ography ▁of ▁Switzerland