▁from ▁the ▁mid - 1 st ▁century ▁BC ▁to ▁about ▁ 4 0 0 ▁AD . ▁ ▁An ▁important ▁factor ▁was ▁the ▁construction ▁of ▁the ▁Roman ▁Rh ine ▁Valley ▁Road ▁between ▁the ▁provincial ▁capit als ▁Main z ▁and ▁C ologne ▁along ▁the ▁left ▁bank ▁of ▁the ▁Rh ine , ▁both ▁on ▁the ▁plate au ▁( n orth bound ▁from ▁Rhein b öll en ) ▁as ▁on ▁the ▁left ▁bank ▁in ▁the ▁Valley ▁( the ▁route ▁of ▁the ▁modern ▁highway ▁Bundes aut ob ahn ▁ 9 ). ▁ ▁The ▁Rh ine ▁was ▁the ▁border ▁of ▁the ▁Roman ▁Empire , ▁which ▁is ▁why ▁the ▁road ▁had ▁to ▁be ▁constructed ▁on ▁the ▁left ▁bank , ▁just ▁inside ▁the ▁Empire . ▁ ▁Tra ces ▁of ▁significant ▁road ▁construction ▁have ▁been ▁identified ▁near ▁St ah le ck ▁Castle ▁at ▁Bach ar ach . ▁ ▁The ▁cities ▁of ▁B ingen ▁( B ing ium ) ▁and ▁Kob len z ▁( Con flu entes ) ▁are ▁the ▁sites ▁of ▁early ▁Roman ▁for tr esses , ▁and ▁Ober w es el ▁( V os ol via ) ▁hous ed ▁a ▁Roman ▁Mans io . ▁ ▁The ▁for tr esses ▁protected ▁agricult ure ▁and ▁ ▁natural ▁resources ▁against ▁the ▁German ic ▁tribes ▁of ▁the ▁Ten ct eri , ▁Us ip etes , ▁Men ap ii ▁and ▁E bur ones . ▁ ▁The ▁agricult ural ▁settlement s ▁in ▁the ▁hinter land ▁provided ▁for ▁the ▁people ▁in ▁the ▁cities ▁and ▁military ▁cam ps . ▁ ▁The ▁Rom ans ▁used ▁the ▁Rh ine ▁for ▁sh