▁the ▁ 4 th ▁century ▁BC ▁or ▁early ▁H ellen istic ▁period , ▁the ▁mod est ▁structure ▁represents ▁the ▁oldest ▁known ▁Greek ▁bridge ▁with ▁a ▁vous so ir ▁arch . ▁ ▁Const ruction ▁and ▁location ▁ ▁The ▁Rh odes ▁Foot bridge ▁was ▁un ear th ed ▁in ▁ 1 9 6 6 − 6 7 ▁close ▁to ▁the ▁eastern ▁har bour ▁of ▁the ▁city ▁of ▁Rh odes , ▁the ▁Ak and ia ▁Bay . ▁There , ▁an ▁artificial ▁channel ▁of ▁ 2 . 1 5   m ▁depth ▁ran ▁parallel ▁to ▁the ▁ancient ▁city ▁walls , ▁separated ▁by ▁an ▁ 1 1 ▁m ▁wide ▁street ▁running ▁in ▁between . ▁The ▁side w alls ▁of ▁the ▁condu it ▁were ▁made ▁of ▁at ▁least ▁four ▁layers ▁of ▁por os ▁lim estone ▁blocks , ▁the ▁same ▁material ▁also ▁employed ▁for ▁the ▁arch . ▁ ▁Near ly ▁at ▁its ▁mid point , ▁the ▁canal ▁is ▁crossed ▁by ▁an ▁ 8   m ▁broad ▁arch ▁of ▁w edge - sh aped ▁stones ▁which ▁served ▁as ▁a ▁foot bridge . ▁The ▁cur ved ▁opening ▁has ▁a ▁single ▁span ▁of ▁ 2 . 8   m , ▁identical ▁to ▁the ▁width ▁of ▁the ▁canal . ▁Its ▁surprising ly ▁low ▁rise , ▁in ▁the ▁order ▁of ▁ 1 ▁to ▁ 3 − 4 , ▁gives ▁it ▁the ▁appearance ▁of ▁a ▁segment al ▁or ▁even ▁multi - center ed ▁arch , ▁of ▁which ▁it ▁is ▁the ▁only ▁known ▁example ▁in ▁Greek ▁architecture . ▁ ▁While ▁it ▁has ▁been ▁argued ▁that ▁the ▁foot