 The surface level is almost horizontal : the roadway lies at a height of 20 @.@ 05 – 20 @.@ 55 m ( 65 @.@ 8 – 67 @.@ 4 ft ) above sea level between arches 1 to 20 , and falls slightly in its eastern section , between arches 21 and 26 to a level of 19 @.@ 94 to 19 @.@ 66 m ( 65 @.@ 4 to 64 @.@ 5 ft ) . Since there is no indication of a later sinking of the structure , this nearly uniform height indicates careful levelling and the existence of solid pier foundations . In contrast , the lengthwise axis of the bridge displays often significant deviations from arch to arch . 
